What happens if their system gets triggered and we are not at fault?
What if we win a lot of money and it suddenly becomes worth it for the casino to try to delay us with KYC and blame their security system. Anybody can fake the logs saying you've logged from a different IP.
It's already a norm for casinos to ask KYC when they are withdrawing large amounts of BTC. Once they start asking KYC right after registration, users will already be alarmed for they have no reason yet to submit KYC nor to stay. Gamblers hop from one casino to another hoping for free spins to each.
It's worth it for casinos to delay. So long as they won't get a negative rep from users, they might just delay for months. Its kinda way for casino to ask you to play once again coz maybe this time you'd lost those amount you wanted to withdraw.