I occasionally write stuff for my own use that might be of use to others. There's no downside to me if I release it, and the occasional upside.

Sometimes I need to apply a fix to some OSS project. Contributing helps me avoid having to maintain a fork.

Sometimes I write something at work that may be useful for others and convince my employers to let me open source it, and as a result I am also able to reuse the same software at home or in future jobs.

None of these have deprived me of income. Some of the work I was paid for. Some of it has indirectly led to income.

I find your expression of resentment curious. Their use of your software did not deprive you of anything other than in your own mind.

OSS is freely given, sometimes by people who are paid to do exactly that. The term "unpaid labor" has a specific connotation akin to slavery or indentured servitude. The two are not comparable.

Complaining that someone somewhere makes money (at best, indirectly) from an OSS contribution is the same as complaining that Good Will resold my donation at a profit.

Is this a legal term of art or common knowledge definition? It was unknown to me so I've tried some googling and am turning up primarily volunteer work and unpaid internships under that title. I know wikipedia isn't the greatest source, but over there "unpaid work" is a class of things including both slavery and working at a family business or coop.

It has nothing to do with whatever political axe you have to grind.

It sounds a bit like you're buying a round of beers for everyone in the bar, and then you're upset people didn't compensate you for it.