They don’t just steal the customer money and buy themselves luxury real estate.
The fix guys are in trouble because they were both very corrupt and very bad at creating even the thinnest veneer of plausible deniability.
They were operating a shadow bank and unregulated securities exchange in the Bahamas and Hong Kong.
The media and regulators were willing to take a sympathetic view to all of the openly illegal banking and securities violations while times were good, but they were performing a highline act with no safety net the whole time.
I'm guessing you're not very familiar with games of chance.
So as you said the commingling was a large part of their crime.
But they did commit a bunch of straight up theft of customer funds to pay for marketing, political donations or stuff like houses for the employees.
The game you’re thinking of is roulette. Blackjack doesn’t have colors to bet on.
Putting it all on black is only theft if you lose. FedEx’s founder famously bet half his employee payroll on black and won.
FTX eventually lost.
I definitely consider it akin to theft even if people don't quite want to use the word.
And importantly even if you ignore the fact that people aren't being made whole by the bankruptcy's 100% claim, people still won't have gotten their money back for years. So people are still significantly harmed despite the criminal winning some illicit bets.
The money in your checking account or savings account isn't sitting in a vault, it's being loaned out to other customers of the bank immediately. But when you put money in an FDIC-insured bank account, you have the US Government guaranteeing that you'll get your money back even if the bank's investments of your money go bankrupt. Also, there's a complex set of regulated and audited independent counterparties with transparency and collateral agreements to separate custody, trade settlement, etc.
When you put money into a Bahamas based entity that is simultaneously the bank, exchange, broker, and hedgefund, you get none of these things, and so you just have to wait until it collapses and then hope to get your money back after bankruptcy court in a few years.
But yes, it's frequent enough that I hope it dissuades at least some would-be scammers not to risk it.