Logically, this is correct. Before any bet is even placed, KYC should be required. However if this was the case, a lot less people would use casinos. So instead, the casino lets people play, lets them lose without KYC, and if they win, then ask for KYC. It's malpractice, at best.
This is working very well for the casinos since they are earning huge amount of money from players who are losing on their site.
It's no rocket science to understand that people are eventually going to lose money in the long run.
May be this is why casinos don't tend to ask for KYC initially and let players gamble without KYC.
If they ask for KYC then they will be losing their users but asking for KYC only when players win a lot is a like a win-win situation for them and they are using this method to their best.