They're not like prediction markets. They do exactly what GP says they do: if you win, you effectively get banned (max bet sizes shrunk toward $0). If you suck, they do the reverse and expand your max bet sizes and offer you loans.
These things are so unfathomably antisocial that I earnestly believe every single politician who advances them should be (journalistically) investigated as extensively as is legally possible.
There are lots of places where you can bet against other players now. The older betting markets like Betfair are no longer available in the US, but Kalshi, Polymarket, and others now offer the same kind of two-sided marketplace in the US.