My reasons:
1. Many people use "teaser" titles for their threads, so I look just to see what the thread is about. Yours is a good example. I had no idea whether your thread was about sex, the economy, or something that happened that day. Very often, once I've looked, I have no interest in the topic and so no reason to post a comment.
2. Like many others, I may be interested in the thread topic but not have anything valuable of my own to add.
3. I often check back when I'm interested in a thread. So I may post once, then look at it five or ten more times to see what else has been said - so you see 6 or 11 looks but only one reply for all of them. (And if I did post, I often check to see if anyone responded to what *I* said.)
4. Sometimes a thread is thought-provoking and I want to decide what to post, so I won't reply immediately. So you may see 2 views but only one reply in that case.
5. Frankly, sometimes I don't post because I'm censoring my words, knowing I'd only get into trouble for posting what I really want to say.