I've been in the auto industry for a while now and there's a lot of professional mechanics I know who do the bare minimum work/maintenance to their own vehicles because when they clock out, they've run out of the energy to work on their own stuff and want nothing to do with cars until they're getting paid to do it again the next day. It's not the case with every technician, but I would gander a guess that it's over 75% of them, at least in my experience.
Point being, I would imagine bike mechanics experience the same thing. Regardless of trade, it takes someone truly passionate to be able to go to work all day on [insert skilled labor here] and be willing and happy to continue to do it at home (or wherever really) at the end of the day. I know a small few people like that but far fewer than the ones who just want to do anything else at the end of the day.