I don't have something nearly as popular as these other projects; but if you have a popular project, a potential employer might offer work hours for it to get you as an employee.
Further, as a contributor of some now popular projects with one other maintainer, I can say that I mostly do it for fun. My current employer gives zero-fucks about it but if a new employer were to use it to woo me away, I would jump in a heartbeat.
My employment contract specifically allows me to keep any rights that I do on my own time and equipment that doesn't compete in certain areas -- and enumerates those industries.
Further, as a contributor of some now popular projects with one other maintainer, I can say that I mostly do it for fun. My current employer gives zero-fucks about it but if a new employer were to use it to woo me away, I would jump in a heartbeat.