If you believe in giving away code because that’s open-source prosocial, then open-source adherents will claim that taking advantage of you is ethical, because if you didn’t want to be exploited, you shouldn’t have been open-source prosocial in the first place. And by treating “pay me if you get paid for my code” licenses as treated as evil and shameful, exploiters place pressures on prosocial maintainers into adopting open source licenses, even though they’ll then be exploited by people who don’t care about being prosocial, eventually burning out the maintainer who either silent-quits or rage-quits.
Of course, if OSI signed off on “if you get rich from my source code you have to share some of that wealth back to me” as a permissible form of clause in open source licensing, that would of course break the maintainer burnout cycle — but I’m certainly not holding my breath.