Matching starts minus a player on one team

why when a matchmaking game starts minus a player or when one drops out a new player is not added that is queuing up?
i have noticed that some modes of matchmaking this does happen that a player is added. Why not in ranked slayer. It would certainly even things up some times.

Maybe its like if its in ranked it wouldn’t be fair if someone is getting ranked and they gain a game at the very end and they lose or win, its basically an automatic loss or win that they didn’t deserve, maybe its that but idk