Well... I don't know... From what I've played so far, most people do talk if anyone wants to (unless language problems or people who can't both play and type). However someone has to take initiative and try to make people talk (usually I do that first myself like I say what skills, I will take, what upgrades I'll get, etc). Also from time to time warning teammates about enemy favor items, etc. But I don't do that always. Sometimes I just play a silent game (without any notifications, talks, unless someone besides me starts to talk). It might be too tiresome to talk in every single pug game, but if anyone from team wants to, then I am not against that.
2v2 might increase a competition a bit, so communication might be more important for players, because no one might come to save you, no one might do some upgrades, while in 3v3 it is a high chance that someone else will do upgrades (sometimes forcing not to get any upgrades at all) and you feel much safer.
Oh and also. 3v3 without communication is more challenging, so why not to try that sometimes? 
Then it comes down to understanding your teammates and trusting them (sort of mind reading, which I like 
). But also... There are more teammates in 3v3 who insult you for every single thing you do, and that creates either rages or zero communication... Which lessens the communication in future games...
