You are imagining people in your head. Most serious open source contributions are paid for. Per FSF survey overwhelmingly so.

Because, they are a lot of work. They are not hobbies or kitchen soup two hours a week effort. These require a lot of sustained effort and time, that would either takes time from your paid job, or would make you effectively work 60 hours a week which means you have no other life.

End result is that these are paid positions, so.