There's a fairly big difference between "you're making an emulator for a console we stopped selling anything for a decade ago" and "you are actively cutting into the sales of everything we are currently doing"
Frankly, Im not quite sure what anyone expected. Of course they were going to go after them harder tan usual, especially when they made it pretty obvious they used proprietary code from TOTK. I'm as pro-piracy as they come, but ya still gotta use some of your brain.