It doesn't have to be a prohibition either. Advertising could be banned. Branding could be controlled so it isn't appealing (Provider 1, Provider 2, etc). Parlay bets and "innovations" (which burn customer money 10 times faster) could be restricted. The "concierge" service that preys on the big spending addicts could be regulated/erased.
That's the sort of ban that actually works for society, because it is strongly focused on disincentivizing harmful behavior, while shutting out the black market.
> Advertising could be banned.
I always liked how the offshore casinos would setup a play money casino on their name.net and advertise that on the poker shows. Of course, I imagine a lot of people would put in .com instead and accidentally end up on the real money casino. Whoops.
The other regulation would be acredited gambler thresholds, that limits how much an individual can bet, based on some formula that accounts for a person's income and net worth. You're just not allowed to gamble more than a third of what you legally earned last paycheck or whatever.