All 17 of those years were likely not "good" years for retirement. Probably didn't have enough points to retire in 3 years, and he was only 40, so another decade or so of pretty low wage weekend drill national guard duty may not have been attractive to him, for a small pension after age 65. Or maybe he converted his years into government service equivalents to get more government retirement ("buy out"). Or maybe he had an injury. Who knows.
As an example, a former military person can buy out their years of service if they are currently, for example, VA employees-- to get a higher pension, when their military years alone aren't enough for a pension. The buy out rate is different for every person, based on rank, years of service, government job, etc. (Active duty 20+ years gets their retirement immediately regardless of age; reservists have to wait to age 65+ regardless of what age they retire, after 20 "good" years of points/ service.)