I suppose that the argument that the casinos will give will be a matter of security, but there are those who could see bad intentions in:
1) You lose a lot of money: I do not ask for KYC.
2) You play a lot and win $20; I do not ask you for KYC.
3) You play, win and request a withdrawal: I ask you for KYC.
All we hope is that they are only doing this for security mate but like what these 3 mentioned by you It is an obvious intention in their part to at least delay the withdrawal taken by the gambler simply by asking them to conduct KYC when it is obvious that most players go in their site because they are not asking for Verification or KYC when starting or luring players , but when the winning comes (specially when it is good enough wins?) then this obligation will be asked and if you deny the verification then you'll never get your funds.
this has been an issue from the beginning that's why many of us deny the fact that there are at least single casino site here that does not ask for KYC in any chance.