It’s always a case to case basis when it comes to casino account KYC. I still have my account unverified on BC until now even though I deposited huge amount before and do a lot of withdrawals.
But I do encounter casino ask KYC immediately after few deposits and withdrawal so this KYC thingy is solely based on the casino security preference because they can trigger it anytime. I think they are using the casino activity most of the time for the KYC.
But some casino indeed using it to delay or potentially forfeit the big wins especially if they have suspicions that the account original owner is from restricted country since they knew if users use VPN to hide their IP.
There are several factors that contribute to a casino deciding to whether and who to ask to verify his or her account, just like you mentioned about casinos knowing when a user is making use of VPN possibly as a way to hide their true ip address, specially when the gambler is gambling from a restricted country, such a user is likely to trigger the kyc verification system faster then other persons who are not using VPN to play.
And also myself, my Bc.game account is also still unverified, I am not a very frequent gambler though, but I definitely over time have played alot on this casino, withdrawn some nice sum of amount of money which ordinarily should trigger the kyc system if it was on any other random casino, but that didn't happen on BC, this goes to show that maybe Bc is not really heads-on on collecting customers data, but care more about giving customers the satisfaction they need.