I’m gonna play devils advocate, but I truly don’t think people are “quitting” as much as they are crashing/dropping.
I’ve said it before, but I’d bet a month of store items that the ranked “leaver” issue will sort itself out by a significant amount if the ability to rejoin matches was implemented. Which it should’ve been at launch.
Had 3 separate instances of friends who’s game crashed/experienced internet issues/pc crashed at various intervals within a match (prior to loading in, within the first 5 minutes, middle of the match).
In these cases, they were devastated they couldn’t rejoin and try to salvage the match and they’d be punished despite circumventing the issue and getting their game running in time to rejoin.
Of the short list of features carried over from legacy Halo titles, this is the one that makes the makes the least amount of sense.
The infrastructure exists to enable this (joining friends in casual modes), it should be a priority to add this to ranked as well.