Because there is so much hysterics about comments here. C'mon, we're just people. We can't handle everything... sometimes even replying to comments.)
I always try to reply to everything, but sometimes comments from people are so... empty in context that I simply don't have anything to answer.
For example, those "cute", "awesome" comments. I often reply with thanks thanks thanks thanks over and over again, but sometimes i simply don't feel like it. xD
But all aside, I see your point.