People do use in-game voice chat, but because people who can successfully integrate with online communities and communicate with people politely, have usually found groups of likeminded players to play with.
Generally speaking, the people you find present in public voice coms, are people who are either new to the game (nothing wrong with that) or people who have struggled to find a community of people to play with. One of the most common reasons they struggle to find people to play with regularly, is because they're toxic themselves. As such I think that you find a disproportionate number of people in those voice coms who are really unpleasant. And with all of the larger friendship groups sticking to their own private chats, theirs rarely anyone to call out their abusive behaviours when they do start to pick on someone.
With all of that said, there's also a third type, the guy that just keeps his mic on to mouth breath into it or so that you can hear his kids screaming in the background. You ask in the open channel, 'hey, anyone got a mic?' and try to get some team work going, and they ignore you for the whole game.
