Ah, the old -Next emulators - FBA, VBA, Snes9x, FCEU, and Genesis Plus GX. Good times.
I recall using this emu many years ago, and I never figured that out, either.
The answer is obvious - why use such an ancient, outdated emu? Granted, during RetroArch's first few years the standalones were probably a better option. But that hasn't been the case for at least 5 years, probably more.