Why is it considered acceptable to leave fanfic authors criticism, as opposed to fanartists?

This isn't a vent as I rarely get unsolicited criticism, myself. But it's just something I've been curious about and I don't exactly have any friends that write who I could discuss this with.​

It's oftentimes seen as rude to give fanartists negative feedback regarding their work since they're considered hobbyists (Excluding those cruel Youtubers that used to make fun of online artists on Deviantart, etc).

But inversely, why are fanfic authors sometimes considered being in the wrong for being adverse to criticism (Constructed or otherwise). At the end of the day, fanfic authors are hobbyists as well. And even if they're not, it's just a hobby. Some writers and illustrators aren't looking to improve their craft. They just want to have fun with the series.

I think the closest thing I could come up with is that in the current state of the internet, fans who create art, fanfics, etc. are sometimes held up to the same status as content creators?​​​​