Go back and read the reactions to forced public matchmaking. 'This isn't fun anymore' 'I don't want to try hard to win'. These are people who want to be a minority in an fps game, where they can still get to shoot people and have an impact without being at risk for helping you lose.
I've seen a lot of friends get into OW, enjoy it, then slowly realize it's like any other moba. You play the wrong class, you don't perform as expected of the average player. The same goes for matchmaking. You go from being 1 of 12 to 1 of 6, you have to do twice as well and in most cases also be the only player of that class. That alongside with suddenly having to be on voice and interact with strangers is jarring to most.
Even if you do want to play medic, you're one of the most important components of a team. Can't drop ubers, can't miss arrows. Useless shit scout on the flank? "Oh I'm having a bad day". There's no easy way around this other than to be a ballsy player, and a hat simulator doesn't motivate that kind of behavior.
That said, it's also just not a competitive format. Competitive cs:go? Literally the same map and setup. In that way the new 6v6 MM is pretty nice for introductions, but obviously it's still shit. There really isn't a way to go about this without diving in head first. Playing with other noobs is probably the easiest approach, but hey. Who wants to do that.