I don't mind stale repos when it comes to emulation, because nothing changes (except the host/build ecosystems) so there is less to keep updated. In the case of the NES, the last game released was in 1995.
NES is a little unusual in this respect because the vast majority of cartridges have "mapper" hardware that must be emulated, and there has been a more-or-less continuous trickle of unlicensed cartridges over the years, some of which have unique mappers. If memory serves you can get to something like 95% compatibility with the few dozen most common mappers, but then there's a pile of oddball mappers that are each used by 1 or 2 games (many of which are just pirate hacks of a licensed game).
Yeah a stale repo isn't bad as long as there aren't outstanding issues to be worked. It is still a bad sign in evolving tooling environments like java c++ or rust, but lisp is pretty stable at this point too...