I saw some people asking for demographics of the area and thought maybe I could provide some insight based on what I know about the area (and I frequent it as a lover of the old Gothic revival and Victorian architecture) One of the oldest areas in Cleveland, Ohio City is a strange area and has been the recent focus of a lot of rehabilitation projects. As a result, you may have one street that seems ... well ... new. The main road has shops, bars, condos, and while it used to be a predominantly Hispanic area, they've been kinda pushed into one specific area while more people move in lured by tax breaks and home renovation loans.
The areas off the the main roads can get very sketchy very fast. It's not an area I'd frequent at night. There are about 9,000 people in the area with a median income of $20k / yr. The area is very poor. I suspect the only thing that drags the median income up to that number are some are the newer areas that have become popular with the "hip" "artist" "yuppy" types.
There is A LOT of crime in and around Ohio City.
http://spotcrime.com/oh/cleveland/ohio+city-west+side Mostly robbery, thefts, assaults, and drugs. Lots and lots of drugs. Murder, random shootings are less common but not at all unheard of.
Add to this that Cleveland (last I checked) was literally the foreclosure capital of the country. While the home Amanda Berry was found in may SAY it's valued at $30 some thousand dollars , I guarantee you it couldn't be sold for anything over $3-5,000. There are literally thousands of homes boarded up by banks, everywhere. In fact, banks have taken to just demolishing them to keep them from becoming flop houses for drugs and prostitution OR in some cases, banks are letting the current residents stay cost free just to keep it occupied and safe. Driving down the street in some of these areas there may only be 2-3 homes that are occupied in 10-20 homes.
This may account for how many people didn't see anything going on at this house. There may not be many occupied homes in that immediate area. The street this is located on sports a lot of boarded up, dilapidated, seemingly unoccupied homes.
It's also an area where you mind your own business. You sure as heck don't go sniffing around or calling police into your area unless someone has a gun pointed at you. A naked girl in a back yard would hardly be pause for thought. Hearing screams would garner the thought "Someone must be beating their wife again." Calling police is likely to draw attention to your own crimes. We all saw Charles jump when he heard the siren. There was a reason for that. The man wasn't kidding when he said a neighbor said he had HUGE TESTICLES... because in that area, doing something like he did could easily have cost him his life.