Once the big income stops, they cannot accept the fact that they need to cut way back on their extravagant life style. And, many will owe significant amounts in back taxes which will catch up with them.
Many athletes and entertainers simply do not have the smarts and discipline to manage money. A large percentage of them will encounter financial hardships after their careers wind down.
Its a lot easier making money than it is keeping it.
I read about a financial consultant, who served clients that had come into sudden wealth and were having trouble managing it. It happened that he had been approached by, and taken on advising, one pro football player, in addition to his regular roster of doctors and such.
The guy was making millions, but of course he had to concentrate on his game rather than his property. Priorities, and all that. Meanwhile, his family were going out and splurging on houses, cars, and more, expecting him to pay for it. His money was "their" money, of course.
They had gotten used to calling up his accountant and asking for wire transfers all the time, the accountant would call the player to get his approval, and he would just approve. No time to do otherwise, and besides, the drama that would ensue if he refused, well, you know.
So, in effect, the consultant was charging for his services to be the "bad guy" who says "NO!"
Somebody's gotta do it.