I know a lot of people do! Even on questions that don't need personal information or experiences that can be uncomfortable. I'm glad that I can not allow anonymous people to comment but not because some are scared or embarrassed but because some people hide who they really are. Most of the time trolling and bullying so nope sorry but answer anonymously on my questions, plus they're not even uncomfortable questions to answer. That's just me, I hope I didn't sound me but I was anonymous when I started but lost that fear of judgement, I'll just answer a question with confidence or just pass it up and move along.
Because you touch yourself at night lol jk. I guess being anonymous prevents judgement either of the pic, profile, or comments. Plus, a lot of these questions are personal, or kinky. Sorry for my childish comment in the beginning of this response. Oh well :P
I think what makes people go anonymous is because of the fact that whatever you post is here forever. If you make a post or a question, there's nothing you can do once you accept. No deleting. Anonymity makes it a little easier to ask and answer questions without having your persona attached to it, especially if they're dealing with something personal that has a lot of specifics that somebody they know (or even worse, relevant to the topic they're discussing) could come across. I found this site originally because of Google searches that showed up with relevant questions. This place is a hot-spot for Google search. Who knows who could stumble on your things, jsut by typing in a question on Google? Though the internet is a wide and vast place, specifics, especially put to a username and a face, can definitely give yourself away in some cases.
Because people are to scared to say what they stand for or mean. They want to hide behind a web form. I would bet that 90% of the people on here talk a big game but wouldn't say any of this in real life.