You're making too many assumptions from such broad data. No, houses don't generally fall apart within 50 years. But most houses built 50+ years ago are small by modern standards, and many have been torn down and redeveloped since then. For the ultimate peek into this phenomenon look at Tokyo, where the lifespan of a house is short and any given plot of land is rebuilt several times per century.
Also, of course, one should keep in mind demographic shifts. There are many small towns (and even some city suburbs) with cheap empty houses that many people would never willingly occupy because there are no jobs there.
Also areas like East Cleveland that have a notorious reputation. Even if in that particular case the city was built by John D. Rockefeller, he is even buried there.
Ah yes, East Cleveland. One night I was biking home, one of the locals took note of my weakened position with a flat tire and that my skin color denoted I was not from the neighborhood, and they put a gun to my head. If you buy there, I recommend availing yourself of Ohio's constitutional carry provisions.
