Because they don't. If you're talking about straight tournament winnings and sponsorship money (no action money), only the top 5-10 in the world make a decent living. But, there are a lot of players who win a lot of money outside of tournaments.
Baxter...You're correct, although the number could probably be closer to a couple of dozen, if you include the world. Even gambling doesn't make much money, as you'll still have expenses, and most of the time, money won gambling pool is lost gambling on something else (horses, dice, cards, poker, sports betting, etc.). The few players that make a decent living actually playing pool, work hard for it, and deserve every dollar.
Because they don't. If you're talking about straight tournament winnings and sponsorship money (no action money), only the top 5-10 in the world make a decent living. But, there are a lot of players who win a lot of money outside of tournaments.