Why don't people sue gun manufacturers every time somebody is murdered?
Because gun makers lobbied congress to make it specifically illegal to do so. Even though unscrupulous practices by said gun lobby is responsible for probably hundreds of thousands of needless deaths.
Or vehicle manufacturers each time an accident happens?
They get sued for accidents caused by defects quite often.
Why don't they sue PC manufacturers for producing the hardware that led to the emulator?
This one is perfectly analogous to the Nintendo tomfoolery, though.
Suing Yuzu for piracy seems incredibly fucking stupid and nonsensical, but I'm sure the Neanderthals in the courtroom will side with Nintendo.
Happened with Mega and countless torrent sites so yeah, you're probably right 😮💨