Lots of FOSS developers support themselves with lucrative jobs or contracts they received on the basis of their reputation within the FOSS community (conference circuit, online forums, professional network, etc.) and otherwise mainly develop for the clout. Social consequences can be very effective in this way. It isn't quite like being blackballed but you really can't piss too many people off before those contracts start disappearing. Network effects work in reverse too.
“FOSS developer” is hardly a career. Nobody is losing out on income by you blacklisting their projects.