Why do people watch questions without commenting??

Because they suddenly realize that they don't know the answer to the question, or they see that someone else has typed the same answer they were thinking of, or they came to read other people's answers because they're curious about the answer.

[c=#BF0080]Because I'm not interested in answering the question.. maybe I don't have a good answer so I want to see what others comment.. I do it often.[/c]

Cos they're being nosey maybe?

Sometimes I take a peek just to see if the posts are actually bad enough to give me cancer

You can't comment on everything.