For a professional writer, doing a fanfic is a lot like a musician doing a cover song for a compilation album. It's a bit of fun and a chance to do something a bit different, put your spin on a song you enjoy, and pay your dues to your inspirations. You crank it out in a week or two, maybe record a goofy video, then go back to writing real, serious music.
What you don't do is spend over an entire year working on it as your sole creative activity. If that's what you're doing you're not a professional, you're a hobbyist who works on it when they have the time.
There's a reason why releasing a covers album is the last thing many bands do before they break up - it's a sign that their creative process has totally broken down and all they can agree on is to cover songs that inspired them when they formed the band - a time before they started hating each other.
Pat is basically writing the literary equivalent of The Spaghetti Incident, except Gn'R were actually successful before they started fighting. Also they still wrote, produced, recorded and released it in less time than Fatrick Porklinson has taken to still not finish his dumb fanfic even though they could barely bring themselves to speak to each other.
