at what point does a crypto book actually ask for kyc? trying to map this

i've been using a few different crypto casinos over the last few months just splitting my roll between stake, sportbet, and rollbit depending on who has better odds for whatever i'm betting that day.

always thought the whole point of crypto books was that they left you alone, but i hit a kyc block on rollbit last week after trying to pull out about 1200 bucks. it wasn't even a massive win, just a slow grind up. meanwhile i've done bigger single cashouts on sportbet with zero issues so far, and stake hasn't triggered anything yet either but i know they do it eventually.

just trying to figure out what actually sets it off for these sites. is it a cumulative withdrawal limit, a single big win, or do they just randomly flag accounts when they feel like it? anyone got actual numbers on where the threshold usually sits for different books?