If you ARE in a top writing school... well... you do EXACTLY THE SAME THING.
Video games. Comics. VFX in movies. Animated movies. Admittedly there are more people looking for a lot of those jobs than there are gigs. But if you find a good gig and keep it going, you can have a pretty nice life. The connections you make in school can help you find some of these jobs, but so can a solid portfolio. Nobody cares where you went, just whether you can show up and do your part of whatever multi-person, multi-year job you're involved in.
And these days there's also Patreon. There's a few people making multiple thousands a month drawing stuff on there. Mostly porn. And there's a lot more people making smaller amounts for various projects. Including me; when I'm in the groove of cranking out eight pages of my comics over a month, I cover most of my rent.
Gallery art? Sure, that's one way to make money with your art. But it's far from the only one.
The concept of for profit school obviously is recent compared to the idea of writing a novel so the class of novelists who didn't go to novelist school obviously contains everything before the student loan boom.
Stephan King, former English teacher and janitor.
Issac Asimov, former biochemist
Umberto Eco, former philosophy degree followed by TV/Radio editor
J.K. Rowling, former BA in French who preferred to read English Lit and worked as a secretary, clinically depressed and unemployed
Hunter S Thompson, former high school dropout, journalist with some audited journalism classes
Ernest Hemingway, former high school grad, served in WWI, journalist with no higher education.
I'm sure there's someone out there with best sellers or Nobel prizes AND went to a writing school, but an anecdote or two proves little.
And that is just one school. If you throw in all the other top programs you are looking at thousands of writers who are pretty much all top earners in their field. Sure, you might be the next Ernest Hemingway or Hunter S Thompson but I think in both cases what you are looking at are writers who filled a certain ideological void in Cold War america that perpetuated certain myths about creativity that were politically fashionable and the market for presenting yourself that way in a now highly professionalized writing world (after the student loan boom) is very very small. People just aren't looking for another Hunter S Thompson to wander around drunk spouting scandalous opinions and having counter cultural experiences. Same with Hemingway: we get it... Men struggle to grasp the duties of masculinity in a world that is fraught with danger. Yawn. There just isn't any material left to write about in those areas and you have to go to school to learn how to get out beyond those bare bones topics by studying past writers and meeting good current writers. Same with "Art" in my opinion. I mean sure you MIGHT be another Basquiat or Banksy but it's been done.