Exactly like all software developers who thought they were going to make games or some world changing application at least in their own time, and then five years later they are just logging out for the day and playing games or streaming crap all evening like everyone else.
Given how many great open source projects there are, some developers actually do that. Just not me and you bro.
A lot of FOSS is maintained by people who are getting paid one way or another to maintain it.
And a lot of FOSS isn’t.
Same applies to basically anything.
Driving is awesome, but when you are driving because you are commuting, or you have to drive your kids to kindergarten/school it becomes a chore and you no longer enjoy it.
I love programming. But when I have to do it for someone else to earn a living, and do it in a specific manner that they dictate, it feels like a chore and I no longer enjoy it.
Having a workplace that is fun and enjoyable isn't about doing the thing you love. It's about a lot of other things, such as the people you work with, the company culture, how much freedom and choice you are granted.
