If you suck at fanfiction and write a 10 page story called "Cloud and Tifa's first date ^_^" then we, your audience, know that you cope with your loneliness and sexual frustration by projecting your fantasies onto video game characters.
If you submit a shitty, FL techno schlock fest here, all we know about you is that you aren't adept at making music.
Writing tends to give people more insight into who you are as a person, ergo you are more vulnerable, ergo you are at a higher risk of not being perceived as cool, ergo you will probably be made fun of.