Fanworks are considered low art because we make and distribute them for free. (Also because we are mostly young, female, queer, or all three, but mostly because we refuse to monetize what we do in a society where monetary value is the only value worth considering.)
I tell you for free what adventures I think Doctor Who or Sherlock Holmes should have, and Iām a nerdy loser with too much time on my hands.
Stephen Moffat convinces the BBC to give him money to tell you what adventures Doctor Who or Sherlock Holmes should have, and he becomes the most celebrated television producer in the UK.
And speaking of monetization: E.L. James forever destroyed any hope of fanworks being treated with respect by mainstream culture when she published a harmful and poorly-written fanfic-with-the-serial-numbers-filed-off that became a global phenomenon. (But Iām sure you already knew that.)
Other than that, making fanart and fanfiction is pretty much completely awesome. š