Even though Microsoft deprecates versions of Windows, they often keep supporting the APIs used for insanely long periods of time. Open Source software doesn't really have the incentive to do this unless "forced" by leadership or a standards body (and even that isn't entirely well enforced, how deviated from Posix are we now).
Java may be similar to a cross between these - as old versions of the JDK continue to be supported and developed, but I assume there's money flowing somewhere to do so.
I work on a number of projects but they're all relatively small so even if the money was coming in it wouldn't be enough to hire someone / quit my job and that means that you're in a dynamic where what'd help most is contributing developer time but that's a lot harder than making a purchase for most organizations. If I offered paid support (or sold books or trinkets) it'd almost certainly bring in 1-2 orders of magnitude less than it'd need to transform the project structure.
That's basically the point I'm making. Paying $75 for printed documentation is easy to justify if your job involves Perl. If four developers work on Perl code, that's $300, which is nothing to the company and a lot better than the $0 they're getting now. Another example would be prioritizing bug fixes and new features.
The bigger problem to me is that maybe I could do that for Perl but it’d be even harder to say I need printed docs for every single CPAN module used on a project. Maybe if the core Perl team gets a ton of support they can spread some around but that’s tricky to match to the projects most in need.
Hiring developers can help in the sense that they'll probably cover many of the needs but that runs into a problematic dynamic where companies contribute things they need but not contributing to unrelated maintenance, which can actually increase the amount of labor on the open source team being asked to review and merge their contributions if that doesn't remove some of the other work.
One argument is that Red Hat is a good compromise for many companies: your accountants can easily write a check for RHEL & support and they employ hundreds of people who contribute to a wide range of projects. Services like GitHub Sponsors are another vision for that but I don't think we've hit a good balance which doesn't result in a major project getting resources while a lot of smaller pieces languish. Umbrella groups like the Django Software Foundation are trying to help with that but I think that's still a work in progress.