Emudev is largely a hobby field. It takes skills from many fields to accomplish. You need the combined efforts of hardware engineers, reverse engineers, diligent documentarians, software engineers with specialized skill sets, etc. Everyone building on top of each other.

You'll see one-person operations, but they're usually relegated to older hardware and they still utilize documentation from many disparate sources. Even nesdev wiki was built on top of 6502 researchers, Taiwanese clone manufacturer reverse engineers, decappers, older NES emulators, heaps of existing documentation, etc.