Sometimes open source helps. SQLite3 is a good example. Being open source (and very good) helped it become one of the -if not the- single most-used pieces of software in the world, but having a closed-source 100% branch coverage test suite helped establish a monopoly on development of SQLite3 and prevented hard forks. End result: big tech had to sign up for the SQLite Consortium. It's... not a unicorn, and I've not idea how much D. R. Hipp and friends get paid -- certainly they get paid enough to continue doing their awesome work, and maybe they get paid like the rock stars that they are, but probably nothing like what they'd be worth if they could really monetize SQLite3 and IPO. The SQLite devs are probably very happy, is my guess.

But yes, on the whole it's true: most open source projects aren't SQLite, and most aren't going to many any money just because they are open source. Open source is a business tool.