That's because Stack Overflow is not a discussion forum. It is, in fact, quite the opposite. Think back; remember the time when you actually got usable, timely help on a forum? Can't think of any? I didn't think so. Why? Because forums are flooded with useless, mindless crap, like users who can't be bothered to form complete sentences, who can't be bothered to do fundamental research or learn the most basic skills of their craft, who want someone to write their program for them, and who have an unbridled sense of entitlement.

It's not the discussion Stack Overflow seeks to squelch; it's the noise. Unfortunately, discussion is one of the things that attracts noisy posts, so it's not exactly something that's actively encouraged.