If they're famous writers, they spend the money they made from their book rights, advances, and the luckier financially, movie and tv deals. I mean, Stephen King had enough money to spend 10 lifetimes to leisurly write a single word a day by 1990 already.
If they're not so famous, the have regular day jobs, or usually writing related side gigs, like writing articles for magazines (at least back when this made you a livable wage), teaching literature, and so on.
Others are independently wealthy, or have spouses who support them.
And some still live in poverty and make it day to day, with random gigs and the kindness of strangers.
I know it's not your main point, but writing for magazines is almost one of the only viable ways to "make it" as a writer/journalist nowadays. Far better than papers/online outlets most of the time.
Or doing writing-related day jobs like writing/editing company stuff and the like. With pretty rare exceptions, writing what you want to write for yourself isn't a sustainable job.
I had been assuming that at least one of Kornbluth or Pohl had been working as a copywriter to pay the bills and that The Space Merchants was a kind of revenge. (similar to how At the Bridge seems to have been inspired by Böll's stint in a statistics office and the Retief series by Laumer's work for Foggy Bottom)
(EDIT: "Cordwainer Smith" worked PSYOPs for Uncle Sam, and pointed out in a textbook that as psychological warfare operators make their career in being economical with the truth [he wrote several decades too early to have "spin doctor" in his vocabulary] one should not rely on their self-evaluations of their own effectiveness. I wonder if this were a dig at Bernays, who seems to have been willing to push his own brand at least as hard as he pushed those of his clients?
Finally, William Faulkner's resignation from his post office day job: As long as I live under the capitalistic system, I expect to have my life influenced by the demands of moneyed people. But I will be damned if I propose to be at the beck and call of every itinerant scoundrel who has two cents to invest in a postage stamp.)
> When I tried to get out of bed today I simply collapsed. There’s a very simple reason for it, I am completely overworked. Not by the office but by my other work. The office plays an innocent part in it only insofar as, if I didn’t have to go there, I could live in peace for my work and wouldn’t have to spend those 6 hours a day there, which have so tormented me that you cannot imagine it, especially on Friday and Saturday, because I was full of my concerns. In the end as I am well aware this is only chatter, it’s my fault and the office has the clearest and most justified claims on me. But for me it is a horrible double life from which insanity is probably the only way out.
So did Dean Koontz. I don't remember if they agreed upon one year or five years for him to make a living at it before he would give up and get a regular job if he didn't succeed. What ever the time period they agreed upon it worked out for him.
King was also a schoolteacher for years. Tolkien was a college professor (and famously wrote the opening lines of The Hobbit on the blank side of an exam paper).
If they're not so famous, the have regular day jobs, or usually writing related side gigs, like writing articles for magazines (at least back when this made you a livable wage), teaching literature, and so on.
Others are independently wealthy, or have spouses who support them.
And some still live in poverty and make it day to day, with random gigs and the kindness of strangers.