When someone leaves a match after the match is completed and they queue for a match they should be put in the queue.
The current system doesn’t actually do that and wastes a significant amount of player’s time in the long run and potentially puts players into matches with people they don’t want to play with again.
Depending on how exactly it works it may also be incentivizing leaving a match at the very end which can shoot teams in the foot and annoy people that are then sent backfilling into a defeat screen.
Source: