I think people might be scared to comment is one reason. I have seen many times where people complain about comments that do not contribute. I comment when I feel I have something to contribute. Sometimes the comment is to show appreciation or try and give motivation. I have seen people complain about the appreciation comments though.

Another reason I think people don't comment is that they treat is like its TV. It's taking the place of the TV for many people. I am very guilty of this I have to admit. It is nice at the end of the day to be able to just sit and watch your smiling face and not care or think. I have to think too much when I type. It took me 20 minutes to write this comment with my horrible grammar and typing. I have to proofread it 20 times because my brain moves to damn fast and I can't understand what i just typed. I guess this is one of those contribute comments. Have a great day!