"The argument that a videogame device manufacturer or a videogames developer can make against emulation is quite simple: emulation constitutes IP infringement, specifically infringement of copyright law and potentially of trademark law principles," says Purewal.
"IP law is not set up to recognise emulation, and consequently almost any type of emulation runs the risk of infringing IP law in some way, shape or form.
"In fact, it gets worse for emulators, because specific laws were passed in the 1990s and 2000s which were specifically designed to stop different types of piracy. But they also potentially stop emulation. These were called
'technological protection measures' or 'TPMs'. So many countries have TPMs as part of their IP law. And so, the basic IP law position, plus the specific legal changes introduced to combat piracy, all mean that the basic legal position is against emulators."
https://www.techradar.com/news/gaming/are-game-emulators-legal-1329264
And if that doesn't work they can just tie you up in court for so long you go bankrupt.
https://en.wikipedia.org/wiki/Bleem!#Closure_of_Bleem!