I think it's because of location. DFW is a huge airport in terms of passengers. But , to get to DFW you have to come through one of the ' port' ( i believe this is the term ) airports for international travel. Anyone flying in from that direction, like Africa or Europe, has to go through NY or DC or ATL to go through customs and then hop another plane to get into the more interior airports. Correct me if I'm wrong anyone who knows better. tia
There is a long list of International Airports in the USA:
United States
Akron - Akron Fulton International Airport
Albany - Albany International Airport
Albuquerque Albuquerque International Airport
Alexandria - Alexandria International Airport
Alice - Alice International Airport
Allentown - Lehigh Valley International Airport
Anchorage Ted Stevens Anchorage International Airport
Atlanta Hartsfield-Jackson Atlanta International Airport
Atlantic City - Atlantic City International Airport
Austin - Austin-Bergstrom International Airport
Bakersfield - Meadows Field
Baltimore - Baltimore-Washington International Thurgood Marshall Airport
Bangor - Bangor International Airport
Bellingham - Bellingham International Airport
Billings - Billings Logan International Airport
Binghamton - Greater Binghamton Airport
Birmingham - Birmingham-Shuttlesworth International Airport
Boston Logan International Airport
Brownsville - Brownsville/South Padre Island International Airport
Buffalo - Buffalo Niagara International Airport
Burlington - Burlington International Airport
Calexico - Calexico International Airport
Casper - Casper/Natrona County International Airport
Charlotte Charlotte/Douglas International Airport
Charleston - Charleston International Airport
Chicago - Chicago Midway International Airport
Chicago - Chicago Rockford International Airport
Chicago O'Hare International Airport
Cincinnati - Cincinnati/Northern Kentucky International Airport
Cleveland - Cleveland Hopkins International Airport
Columbus - Port Columbus International Airport, Rickenbacker International Airport
Corpus Christi - Corpus Christi International Airport
Dallas/Fort Worth Dallas/Fort Worth International Airport
Dayton - James M. Cox Dayton International Airport
Daytona Beach - Daytona Beach International Airport
Denver - Denver International Airport
Del Bonita - Whetstone International Airport
Del Rio - Del Rio International Airport
Des Moines - Des Moines International Airport
Detroit - Detroit Metropolitan Wayne County Airport
Duluth - Duluth International Airport
Eagle Pass - Maverick County Memorial International Airport
Edinburg - South Texas International Airport at Edinburg
El Paso - El Paso International Airport
Erie - Erie International Airport
Fairbanks - Fairbanks International Airport
Fargo - Hector International Airport
Flint - Bishop International Airport
Fort Lauderdale Fort Lauderdale-Hollywood International Airport
Fort Myers - Southwest Florida International Airport
Fort Wayne - Fort Wayne International Airport
Fort Worth - Fort Worth Meacham International Airport
Fresno - Fresno Yosemite International Airport
Glasgow - Glasgow International Airport
Grand Rapids - Gerald R. Ford International Airport
Great Falls - Great Falls International Airport
Green Bay - Austin Straubel International Airport
Greensboro - Piedmont Triad International Airport
Greenville/Spartanburg - Greenville-Spartanburg International Airport
Gulfport/Biloxi - Gulfport-Biloxi International Airport
Harlingen - Valley International Airport
Harrisburg/Middletown - Harrisburg International Airport
Honolulu - Honolulu International Airport
Houlton - Houlton International Airport
Houston George Bush Intercontinental Airport
Huntsville - Huntsville International Airport
Indianapolis - Indianapolis International Airport
International Falls - Falls International Airport
Jackson - Jackson-Evers International Airport
Jacksonville - Jacksonville International Airport
Juneau - Juneau International Airport
Kalamazoo/Battle Creek - Kalamazoo/Battle Creek International Airport
Kalispell - Glacier Park International Airport
Kansas City Kansas City International Airport
Key West - Key West International Airport
Ketchikan - Ketchikan International Airport
Kona Kona International Airport
Lake Charles - Chennault International Airport
Lansing - Capital Region International Airport
Laredo - Laredo International Airport
Las Cruces - Las Cruces International Airport
Las Vegas McCarran International Airport
Los Angeles - Los Angeles International Airport
Louisville Louisville International Airport
Lubbock - Lubbock Preston Smith International Airport
Marquette/Gwinn - Sawyer International Airport
Massena - Massena International Airport
McAllen - McAllen-Miller International Airport
Medford - Rogue Valley International-Medford Airport
Melbourne - Melbourne International Airport
Memphis Memphis International Airport
Miami - Miami International Airport
Milwaukee General Mitchell International Airport
Minneapolis/Saint Paul Minneapolis-Saint Paul International Airport
Missoula - Missoula International Airport
Monticello - Sullivan County International Airport
Moses Lake - Grant County International Airport
Myrtle Beach Myrtle Beach International Airport
Nashville - Nashville International Airport
New Orleans Louis Armstrong New Orleans International Airport
New York City John F. Kennedy International Airport
New York City LaGuardia Airport
Newark Newark Liberty International Airport
Newburgh - Stewart International Airport
Newport News - Newport News/Williamsburg International Airport
Niagara Falls, New York - Niagara Falls International Airport
Norfolk - Norfolk International Airport
North Charleston - Charleston International Airport/Charleston AFB
Oakland - Metropolitan Oakland International Airport
Ogdensburg - Ogdensburg International Airport
Ontario - Ontario International Airport
Orlando Orlando International Airport
Palm Springs - Palm Springs International Airport
Panama City Beach - Northwest Florida Beaches International Airport
Pensacola - Pensacola International Airport
Peoria - General Wayne A. Downing Peoria International Airport
Philadelphia - Philadelphia International Airport
Phoenix Phoenix Sky Harbor International Airport
Pittsburgh - Pittsburgh International Airport
Plattsburgh - Plattsburgh International Airport
Pontiac - Oakland County International Airport
Port Angeles - William R. Fairchild International Airport
Port Huron - St. Clair County International Airport
Portland, Maine Portland International Jetport
Portland, Oregon Portland International Airport
Portsmouth - Portsmouth International Airport at Pease
Port Townsend - Jefferson County International Airport
Providence - T.F. Green Airport
Quad Cities - Quad City International Airport
Raleigh Raleigh-Durham International Airport
Reno - Reno-Tahoe International Airport
Richmond Richmond International Airport
Rochester, Minnesota - Rochester International Airport
Rochester, New York - Greater Rochester International Airport
Sacramento Sacramento International Airport
Saginaw - MBS International Airport
Salt Lake City - Salt Lake City International Airport
San Antonio - San Antonio International Airport
San Diego - San Diego International Airport
San Francisco - San Francisco International Airport
San Jose San Jose International Airport
Santa Ana/Orange County John Wayne Airport (from 2011, after Terminal C is built)
Sarasota\Bradenton - Sarasota-Bradenton International Airport
Sault Ste. Marie - Chippewa County International Airport
Savannah - Savannah/Hilton Head International Airport
Seattle - Seattle-Tacoma International Airport
Spokane - Spokane International Airport
Saint Louis Lambert-Saint Louis International Airport
St. Petersburg - St. Petersburg-Clearwater International Airport
Sweetgrass - Ross International Airport
Syracuse - Syracuse Hancock International Airport
Tampa Tampa International Airport
Toledo - Toledo Express Airport
Tucson Tucson International Airport
Tulsa - Tulsa International Airport
Washington, D.C. Washington Dulles International Airport
Watertown - Watertown International Airport
West Palm Beach Palm Beach International Airport
Wilkes-Barre/Scranton - Wilkes-Barre/Scranton International Airport
Wilmington - Wilmington International Airport
Windsor Locks - Bradley International Airport
Yuma - Yuma International Airport
http://en.wikipedia.org/wiki/List_of_international_airports_by_country#North_America