So basically those who don't get bonuses are inactive users and don't have a VIP level so we can assume they have another casino to play and that's the reason why they ignore the KYC, we also know that many gamblers don't want KYC and the only reason to do KYC is a bonus so do not be surprised if they ignore it. Currently Stake.com gives a deadline until December 31, 2024 well, we don't know whether they provide another offer before the last schedule. I personally suspect that stake will offer something in December so that they don't lose many users.
I won’t be surprised if other popular casinos follow the same. It doesn’t make sense for Stake to strictly enforce KYC while other casinos with the same license providers don’t. So, after the deadline, it’s likely we’ll see other platforms also requiring level 2 KYC verification. The only catch is, who knows if they’ll be as generous as Stake, which is giving a $250 bonus to select users? Other casinos might not offer any bonus at all. If that happens, players might end up feeling the pressure without the perks. 
One thing to remember is as what bitcoinhunt3r said above that not all users are offered with the same amount $250 because there are many others with lower amount and I'm sure it depends on VIP level and other factors.
The offer made by Stake is reasonable IMO because they do not want to lose their loyal players and I'm sure what they spent for the offer is worth for long term.
In my opinion, it is just a matter of time because I think sooner or later most casinos will do the same but I doubt that other casinos can offer the same bonus like what offered by Stake but if other casinos also do not want to lose their loyal players then they may try similar thing but maybe less amount or maybe different offer.