It's seems like a combination of factors.
There isn't enough money in pool overall. So, it is somewhat foolish to try to make a career out of it. Nobody put a gun to their heads and made them choose such a career. They knew what they were getting themselves into.
Two, it seems like some guys that were successful didn't manage their $ well. You must be future oriented and realize that these paydays will not be there forever. For example, Strickland must have made a lot of $ in his day from tournament winnings, sponsorship, etc.
Even some "mainstream" (NBA, NFL, MLB, NHL) athletes have gone broke after making over $100 million in their careers. So, some of it is personal responsibility.