I don't. My employer wants our FOSS core software developed, or wants the bugfix/feature in the FOSS we depend on.
I know people who work for free, but use evidence of that to get well-paid contract work.
Even the guy I know working on a scientific library does that to further his academic career.
I'd be interested to know the situation for significant desktop software (Firefox, Gnome, KDE, a video player, media player, LibreOffice).
Few developers work on FOSS full time for free, at least for very long. However, there is a sizeable group of FOSS developers who do full time or large amounts of part time work for far less than market rate, especially those who are funded primarily through donations. You can go to many smaller projects and see the level of donations they get (e.g. the creators of Godot pay themselves $4400/month, and that is one of the most financially successful small open source projects). I would suspect even for the projects you mentioned above, money is far from the primary motivation of the developers, and they could make more elsewhere.
Successful FOSS businesses usually make money off of selling exceptions, (i.e. selling to non-free software companies) or creating a product with per unit cost (e.g. support).
Essentially, Google, Facebook, Amazon, Netflix and so on, have outsourced development to vast amount of unpaid developers; while software focused companies are becoming more and more rare because somewhere, somehow, a bunch of highly skilled engineers think it's a good idea to spend their own time writing something awesome, while at work they complain about how their work is not understood and how management doesn't give a dime about quality engineering. Instead they should deprive these companies of their free labour, group together and build awesome technically written code, and charge money for it.
FOSS projects that tend to be volunteer led, are that way because the developer is scratching their own itch. Maybe I could make money with one of hobbies, but its a risk, and I don't want to spoil something I enjoy so I just develop X in my spare time. I enjoy it, it's something I wouldn't normally get to do and yes as a bonus I can put it on a CV.
Expectations beyond that are unreasonable? You don't have any right to make money from that, any more than a commercial company has a right to make a profit.
And say everyone did what you suggest, its not immediately clear the world would be a better place anyway, maybe google and Facebook only exist because of the existence of Open source....
The obvious solution to this is to use the AGPLv3 license for all or most software one writes, which is what I prefer to do, as it's the strongest copyleft license available currently.
We see in many circles that it's not the hip thing to do, to write copyleft software. No, the hip thing to do is write permissively-licensed software and either not care about companies using it as free labor or complaining about a ''social contract'' that wants to be implied, but never explicitly stated as copyleft does.
I believe the trend towards permissive licensing has been pushed mostly by corporate interests and now we see the result. I believe things would be better if every company had to either share its code as copyleft, write everything itself, or actually pay for other proprietary software it could incorporate into its own. That is, I'd rather Grammarly, as an example, have no real option but to purchase an Allegro or Lispworks license, rather than being able to use SBCL and contribute little or nothing.
Perhaps people want to do something that changes the World for the better?