That assumes the world is zero-sum. If my employer has a code base that I find more enjoyable / fascinating than any of my side projects, maybe the employer does get extra out of me from me putting in extra hours, but I also get more out of him by both delivering what's expected of me and getting to toy around in a code base that I find fun. I might even be improving my earning potential (if the "fun" argument isn't good enough for you) by building skills working on that production code base that I wouldn't by just messing around on side projects. The dynamic is obviously very open to abuse and people have to protect themselves from that, but I don't agree "extra hours = sucker" is universally true.