It's faster, it's safer. You ever played without heal monk in 60+ pugs? They die. All the time.
Reason for high paragon in low content:
People like to be around like-minded people. If I was a hardcore gamer who plays many hours a day every day, I wouldn't like to play with someone who plays less. I'd have the feeling that I am their rusher and they are the leechers. It doesn't matter if that's actually the case.