@Bronsn Only speaking for myself here, but when I leave a game it's probably one of the following:
1. I'm convinced someone is cheating (enemy or teammate) and I want no part of that.
2. It's late game, the match is already lost (yes, I can tell), and I'm doing my squad a favor by not asking them to take the risk involved in a revive or respawn.
3. It's late game, the match is very likely going to go to my squad, but I get put down and, as before, I don't want them taking the risk. I also get pouty about taking a win I feel I didn't earn.
As for people quitting if they can't have their main: I'm all for it. We should be picking our legends pre-game, and then having mm match us accordingly. I only play one legend, I'm not interested in any of the others, and I feel like I've put in my time and earned the right to be Pathfinder. That said, I don't quit matches if somebody takes him before I get him. I play as if I don't give a rat's backside, but I don't quit.
You want quit penalties in ranked? By all means. But in unranked trios and duos? In casual game modes in a free-to-play game? That I'm just not seeing.