1 of 2 things should happen.
Either make it so if you leave a match before it ends and re-queue within a few minutes then YOU are forced to backfill. I don’t care if you have to sit in queue for 15 minutes.
Other option, just make it so you can’t queue for ANYTHING for 30 minutes. If you leave 3 times within 3 hours you get this timeout. It takes 48 hours to clear so leaving again nets you another 30min timeout and resets it back to 48 hours till it clears.