Basically the Great Joe Louis fought himself out of top tier challengers, so that is when he began giving 2nd and 3rd tier fighters a shot at the Title.
When Joe and other Champions of that era fought, the world knew and cared who the Champ was, the Heavyweight Championship was front page news. Nowadays, 99% of americans don't even know nor care who the Champ is, and mention the name Klitschko, you'll just get a puzzled expression just before the dumb@$$es ask if "Tyson's still in there?"

Almost every fighter had some defeats at one time.

Folks shouldn't use that term "bums" in regard to professional fighting men.