Any reputed site don't care either any user leave them for any rule or not. They want to keep safe themselves as well as their users for that reason they may ask kyc. There are a lot users who violates rule of a site as to avoid that types of users they should take kyc too.
If you mean that FJ doesn't care about their users leaving their site because of certain rules, I disagree. They would have gone out of business long back with that kind of mentality in my opinion.
Crypto gambling sites should only ask for KYC for important reasons though some of them request them for pointless reasons sometimes in order to avoid paying out the winnings since many crypto gamblers hate providing their KYC.
There are certainly some places that goes with "my way or highway" situations, because they rather do it the way they want to or go bankrupt like you say if they do not. Like for example I know one other place that forced KYC to every single person who wanted to register and gamble, without KYC you can't gamble there, but for over a year they didn't had ANY KYC at all, so what happened? They went from (just now the gambling number) nearly 17 million bets per day to now 11 million bets, it dropped as much as 5 million bets at its lowest when it first started but some just gave up and rejoined and gave KYC.
So they nearly got bankrupted if those people didn't get back, which shows you that there are some casinos willing to either be good the way they want to, or bankrupt meanwhile instead of actually doing what the customers would prefer, it is a common situation in crypto.