Most of the casinos do not ask for KYC and they have not made them mandatory. But if we see their terms and conditions, they write that in case of any suspicious activity, they can demand for KYC. I don't understand what could be the 'Suspicious' activity. If you won bog amount of money, most casino treat this as a suspicious activity. 
As long as you are losing a big amount, there is nothing suspicious about it but if you win big amounts, all of sudden your account becomes suspicious.
As long as you are losing a big amount, there is nothing suspicious about it but if you win big amounts, all of sudden your account becomes suspicious.
Can you give a specific example which casino do such thing where player win huge amount then the casino considere it as suspicious activity? I do not think all casinos do such thing, so do not generalize it like all casinos around are the same. There must be at least a valid reason (not based on the won amount only). Afaik suspicious activity is not that simple, it can be about the whole activity of the player based on the deposit activity, betting activity/pattern, and some other things.