Gambling websites also required 3+ confirmations around 2013, but now it's reduced to 1+ confirmations looking at how hard it would be for someone to double-spend their coins on the website (there's still a possibility of performing the 51% attack, but the malicious party will waste their resources looking at the current overall hash rate of bitcoin network)
Gambling websites are fairly unique in the regard that no coins actually need to move until you withdraw your winnings. You can play and win dozens of bitcoin, but the gambling site only needs to honor that when you actually withdraw. And so they can just place a hold on any withdrawals until your deposit has enough confirmations. You can deposit, start playing after 1 confirmation, but then not be allowed to withdraw until after 3 confirmations, or something along those lines. This keeps the risk of any double spends to a minimum.
This is not possible with centralized exchanges, since as soon as you start trading the exchange has to start filling orders. If you double spent, they would be left with a bunch of orders they would still have to honor. And so you have to wait for longer on centralized exchanges.