I have some thoughts on this as a career writer who’s friends with plenty of other career writers—but most of those friends write the kind of content discussed here, whereas I'm a technical writer who works on software documentation (hence why I'm on HN :P).
Technical writers do pretty well; we don’t make as much as engineers, but the pay is nothing to sneeze at. My friends who write blog posts, industry reports, and other corporate content (also usually in the software industry) do reasonably well too. But all the other writers I know are struggling.
What’s interesting to me is that the struggling writers have jobs that most people would find more exciting than what I do: they write essays, or fiction, or they’re journalists at Conde Nast publications. Unless you’re a particular kind of nerd, interviewing SMEs and writing quickstart guides is a lot less glamorous than interviewing public figures and having your name featured in bylines.
In some ways it does seem like the perceived glamor of these jobs is a double-edged sword: the allure of what you do makes it less likely that you’ll jump ship to something less exciting but more lucrative (similar to how game industry devs tend to make less than regular software engineers, from what I’ve heard—you can exploit people’s enthusiasm), and the fact that it’s a cool job means everyone else is also trying to do it (also not unlike the game industry—if you won’t take the job for subpar pay, there’s ten other people lined up who will). There’s a lot of competition, and that subtly devalues your own work, even if the work you do is better than your peers’. Also, not at all to denigrate what my non-technical writer friends do, but jobs that are “just” writing get flooded with applicants because everyone thinks they can write. The barrier to entry is, ostensibly, pretty low, even if most people are poorer writers than they realize and even if most writing jobs require skills beyond simply writing.
Although lately I have seen an influx of people with no experience in the software industry or related tools assuming that it’s easy to break into technical writing; I wonder if the job’s been showing up on those “10 Easy Roles Anyone Can Do From Home” listicles or something. You do have to be a competent writer, of course, but half of my job is working on pull requests and building awful little React components for our docs site.