This is nothing new, 27 years ago the Apache web server came out and pretty soon there were lots of web hosting companies using it for free, some of those contributed back to make it better or hired Apache devs to improve it or set it up for them. The same happened with Linux, PHP, Debian and countless other pieces of software. The only difference now is that devs are complaining about it. At least these days with Patreon and other things, there are more ways for people to pay for development time. Check out the FOSSjobs site and wiki for more options.
https://www.fossjobs.net/
https://github.com/fossjobs/fossjobs/wiki/resources