TC: I think the reaction varies, because science fiction is a more commercial genre. There are a lot more people in science fiction whose goal is to make a living from writing fiction by publishing one or more novels a year. And people who enter science fiction generally receive more messaging about fiction writing as a sole source of income than, say, people entering mainstream fiction. The messaging there is different: get an MFA, teach; it’s understood that your teaching position supports your career as a writer. For writers entering science fiction, that’s not really a thing yet. We’re maybe getting there, but the messaging they receive is mostly: Be very prolific.

https://culture.org/an-interview-with-ted-chiang/

So basically most people don't write S/F "just for fun", and I'm pretty sure that was never the case and all the greats and less-well-known greats of the genre were all professional writers.