That’s an over simplification. My job is owning part of an open source stack. There’s countless fun projects in that which aren’t a necessary part of my job but are fun to do out of hours and and still happen to contribute to my employer’s larger goals. Eg, refactor some subsystem to make it faster. Everyone wins, and because the source is open any future employers can see it also. Plus I enjoy working with my coworkers and learn a great deal from doing so: it’sa good environment for such projects.