The surge might be because of dynamic queue
Lots of boosted scrubs in peoples games, they are bad lose lane feed. They basically got boosted and are now relying on the better players they get matched with to carry them every single time they play.
These better players might be thinking screw that, ill crash this game rather then carrying this boosted clown. In the end the better player will still manage to climb anyway but with more of these players dumping the games with boosted clowns in them they will sink into the 5th divisions, after which you won't have to deal with them again.
It's a legitimate strategy to rid yourself of boosted clowns by refusing to carry their asses. It's toxic yes, but so is boosting and their is no other way to drive these clowns out of your games since Riot sure isn't doing anything about it.
So that might be one of the reasons why the increase of leavers is happening
Added bonus with this behavior is that the matchmaking algorithm will try to balance around a 50% winrate and since your tanking games on purpose you will be matched with better players after usually against boosted memelord scrubs, so you can win make em drop further.
Only thing to watch out for is making sure not to over do it, as you will get regular lower priority queue and have to wait 20 minutes b4 every game which kind of sucks so put up with it enough to prevent this from happening and your totally fine.
Though when it does happen it's ok since you will win most of those games since only toxic boostees and players like yourself are in those games and since there is 5 spots for toxic boostees on the enemy team and only 4 on yours, your chances of winning just increased by a lot, since you most likely end up with like minded decent playing teammates.
It's just a cheesy way to troll boosted clowns and make them get demoted twice as fast.