Most of the people that work on emulators do it for fun, not to get paid. Some do, but almost all have other jobs to support them, or are in places in their life where they are supported by other people: children and students, for example.

There’s a lot of work that goes into a modern emulator, for what it’s worth. Obviously there are people that reverse various parts of the console but it’s really an amalgamation of all sorts of talents. Someone’s going to be a graphics expert. Someone is going to be a compiler and codegen genius. Someone needs to work on reimplementing APIs and improving game compatibility. Someone needs to do UI work. Someone needs to port the emulator to platforms people want to run it on. Someone needs to do design, and PR, and copywriting, and translation. For smaller emulator projects many of these roles may be performed by the same person. For a large project it’s really a team of people working together, often organized in an ad-hoc fashion. It’s really a gem of open source development, where people can bring their own skills to the table and make something better than the sum of their parts, all the while improving themselves.