It is stadium for sure
My guess: They have a “maximum queue” time, the longer the queue ticks the more the “I don’t give an f” counter ticks up and at certain threshold it just gives in and matches with whatever fits
Then there are ton, and I mean ton of leavers.
I would say 50% of my games have leaver or are backfill, but then we also have to include games where you have the priority queue which is a clown show, like no matchmaking at all.
So it is not wrong to say that 60-70% of games are an utter dice roll.