Something I have been wondering...Why so many fictitious/anonymous names used?

This is something that has been very puzzeling to me. Most all discussion on Facebook groups and other sites people always use their real names. WHY does everyone in the CANCER SURVIVOR NETWORK USE fictitious/anonymous Names. I created my account with my real name and will stand behind anything I post, I am not ashamed for people to know my name, just doesn't make sense to me.