Junk mail

What is it with the amount of junk mail I get with Hotmail? I have an account with hotmail that I only use to stay in touch with family and friends. I do not use it for anything else and have never signed up for any mailing lists or used it to enter any contests etc...
Every Day I am bombarded with junk mail. I also have a Yahoo account and a Gmail account I use these accounts more often and for everything email groups/lists, contests, shopping, newsletters etc... I get less junk main in my yahoo and gmail accounts combined then hotmail. Why is this? One would think that as the yahoo and gmail accounts are given out on a regular basis they would attract more junk mail.