Don't we have social media coming out our ears?
Why do we need another form of it in our computer games? It seems to me they were popular back in the day because they were one of the very few ways to connect with people online.
Back in D1/D2 days, there were still *chat rooms* and they don't really exist any more. It's an outdated model for most people.
Games are social, and it adds to the enjoyment of the game. The OP is 100% right in saying that it's boring to just log in a game with 4 strangers, play for a bit than leave. Community is important in the feel of a game, especially an RPG like Diablo.
I feel the same way as the OP, and have also played every Blizzard game.