alias_sqbr

I'm less sure why people are more ok with fanartists (whether they are also employed as professional artists or not) selling their fanart without the ok of the copyright holders.

It's because it's less of a grey area, legally. Fan art - especially non-photomanip art done of live-action characters - is seen as non-deriviative work, because doing a painting of Spock is similar to doing a portrait of a random person who happens to be an actor who played the part of Spock. And there's no law against painting portraits of random people.

Writing a fanfic "portrait" of a character, on the other hand, is seen by some as a "derivative work" (and thus illegal under Copyright law) while it's seen by others as a "transformative work" (and thus legal under Copyright law) but even when it's transformative, the legal protection of the fan writer is greater when they don't make money from it. So it's basically safer for everyone if fanfic writers don't try to sell their work.