I do agree that some fighters need to hang 'em up, but we all know that these guys have had lucrative boxing paydays that have seen their better days, so those 7 and 8 figure checks arent coming in as regularly, if at all. So yes, thats why we see them fighting nobodies for any paycheck that they can get, and some of them REALLY just feel that they can compete, so they move forward in doing so. These guys may have big ticket items that are paid for (hopefully), like mansions, expensive cars, indoor/outdoor pools, greedy family members, children/child support, etc...but the bottom line is, all of these things still need to be MAINTAINED.
Not only does shit happen in the sport of boxing, it also happens in life overall...no matter how much money one may have, bad/unexpected things happen to them as well. For instance, you have Hulk Hogan's wife who divorced him and left with a wopping 70% liquid assets and about $8M from their estate that was used during the taping his show years ago. He only got a few million from the house, and he will end up owing her about $1.5M when that settles.
C'mon guys, Hulk is too damn old to wrestle, his body is shot to no end, and will still need money to live and MAINTAIN the things that he does have. Let's not forget how much money he put forth for his daughter's music career (decent move), but again, shit happens, because he had to pull unthinkable figures out of his ass to save his son from being a prison bitch due to that stupid car wreck that he almost killed somebody in.

We can go as far as how Holyfield still has several children in which he STILL has to pay child support for
Back to my point...maintainence is key and sometimes it can bite you in the ass if you dont spend your money right. That surely has to be the case with these guys that cant seem to hang 'em up. I wonder how much utilities cost in a multi-million dollar mansion, hmmm...