Really, FOSS exists to solve problems of the developers, with good user interface sometimes an afterthought for this particular reason, as the developer is the ultimate power user often enough.
The exceptions are the true big projects, but they can end up in the 10 people situation due to sheer size of it. Those people are then usually maintainers, like in Linux. Unless the project starves due to user/developer mismatch, or gets taken over by corporate interest and people start implementing stuff neither the developers nor users actually want, sapping the energy. (I'm looking here at Mozilla Foundation specifically.)