But writing some open source - making your tools (compilers, linters, runtimes), libraries, frameworks, monitoring, sysops/sysadmin tooling, and so on open source is much more profitable, and that's a huge subdomain of open source out there right now.
You can also get back significantly less than what you put in.
Similarly for independent developers. You don't make money off the open-source software itself. You make money by getting your name out there as a competent developer, and then creating a bidding war between multiple employers who want to lock up the finite supply of your labor. The delta in your compensation from having multiple competitive offers can be more than some people's entire salary.