@aral
In 1997 I was the sole remaining active developer of INN 2.0. Millions of users used the Usenet. I did it as my "main job" and made 12k/year (ISC grant). The heavy lifting, installing the software, and many patches, came from the community.
Postfix, qMail, Postgres, Caddy, a good deal of software that drives the Internet, is run by volunteer enthusiasts who do an outstanding job. Heck, Linux didn't feed Linus until 1996 when he joined Transmeta.
More, when Postgres had the install width of Mastodon today, it was "sponsored" by Michael Stonebraker. Later DARPA and the Army paid a good deal of the development costs, but that was when the project had 800k lines of C code and a development team had to be hired to maintain it.
Another one: Redis was, for years, an enthusiast product. Its success came from an Open Governance model in which no BDFL made all the decisions and did all the work. Later, Redis Inc. was founded and started to pay two developers a part time salary. Still, there are few systems out there that are. not using it.
When Matt took WordPress to the next level and "hired" me, he was working at CNet and I was working at Technorati (and later Socialtext). We made no money from the whole thing until much later (I'd left by then to go into medicine).
Mastodon is not that huge a project. It has the potential to be. It can be easily supported by a governance system and volunteer coders. Much bigger systems were.
@atomicpoet