If it was really about IP, they wouldn’t be going after emulators, they’d be going after rom distributors. It’s not like there’s some secret special industry secret aspect to their 8 year old hardware.
There’s IP protections and then there’s whatever this is.
It's just a matter of strategy— their goal is to get people to buy the game who might otherwise use an emulated copy. They aren't doing it for the principle— It's a sale in their pocket and avoids downward pressure on their price from cheaper (free) sources. Agree with their actions or not, attacking the tiny mechanism that makes all roms useful is far more efficient than trying to whack-a-mole with a bazillion ROM sources forever.
Even intimidating ROM sites out of existence only means they'll get distributed elsewhere. It's much harder to run an open source dev project in secret than it is to seed a huge library of ROMS over BT.