Casinos know that if they asked for this information upfront a great deal of players will not bother to use their services and they will move to another casino that does not behave in that way, however I agree that I would like for the policies regarding KYC to be as clear as possible, I think casinos keep this information hidden so scammers do not abuse their policies, and while I can understand that it is also very troublesome that many players that are honest and which only want to have some fun have to reveal their personal information because they triggered the internal systems of the casino, without knowing what they did wrong for them to receive this treatment.
This has been their business strategy for some sportsbookers this recent years and it a wrong way of doing business in my humble opinion, this could as well turn off some of their customers from using the platform, after facing some delayance before withdrawing their funds as a result of trying to pass the KYC verification process and even some will end up not getting their funds after the whole process, this reason is base upon several complains here which I have come across regarding this issues.
Lastly this could be troublesome for customer that do not have means of identification, like in my country getting original copy( plastic card) of your nation identity card is a big deal, so imagine someone coming from this side of the country that finds himself/herself in this kind of situation, that means he might end up not being able to get his funds. The bottom line is that, However they should make it clear to customer coming to use their platform in the first place , while the decision will be left for customer whether to use their platform or not.