Nobody forces them to keep playing if they can't make ends meet, they are not slaves. They can always find the other job just like normal people in normal life do. Is that an easy way? Of course not but -- newsflash! -- life is not easy for billions on this planet. The complaints of Stakhovsky et al. ("Oh, poor me has to get up at 7 am to get practice court") are just laughable in grand scheme of things.
No they are not slaves. They are people following their passion, doing what they love, trying to make their dreams come true. So they should be forced to quit unless they happen to be top 70 material, or are lucky to have another outside source of income to cover their shortfall? Ridiculous. Oh, and billions are starving? Yes they are. That's a wonderfully irrelevant argument that can be applied to anything.