Writing free software doesn't pay very well, on account of it being free.
Maybe I should work for FSF or Mozilla, but I'd really like to make enough in industry to be comfortable far into the future before I forfeit the chance to retire.
Keep increasing your awareness by responding to your answers by asking questions, breaking it down further and further.
For example, I patched Squid and Apache on the job, and those are "free" software. Out of everything I've done on the software engineer side, I hated that one the most, because the code bases were difficult to navigate for me at the time.