Regardless, it costs money to actually comply with laws, do audits, all that, meanwhile you're losing out on a potentially huge revenue stream by not gambling customer funds. As long as things are going well, you'd expect the shady operators to be winning in the short term.
The problem is you are competing with exchanges that make leveraged bets using customer funds and so can have lower fees.
Banks (and crypto exchanges are that for all purposes) have strict rules on what percentage of customer deposits they have to actually hold and what they can do with the rest.
If that fails there is a huge liquidity market, if that fails the fdic (or local equivalent) comes to the rescue and if that fails the central bank (as a lender of last resort) can contain the failure of a single bank. It's far from perfect but history has proven it quite robust.
Crypto (in this case) decided that all those rules are useless overreach.