casino asking source of funds after i finally hit, never cared when i was losing

Just curious if anyone else finds it suspicious how these places only start caring about "source of funds" once you've managed a good run. I’ve been grinding blackjack for a while, taking my losses like everyone else, and nobody ever asks a thing. The minute I actually hit a payout bigger than usual, they want documents and explanations before even thinking about a withdrawal. It kind of feels like they’re happy to take deposits with zero checks, but the second they need to hand something back, suddenly I need to prove where my own money came from.

I get that they're supposed to watch for fraud and all, but the timing is just too convenient. Lost count of times I’ve submitted all sorts of ID just to get an account going, but nobody ever mentioned anything about source of funds until it was time to pay out. Makes me wonder if they’re hoping people just give up and leave the winnings behind. Anyone else get this or is it just me noticing it more lately?