Again not saying it's a good excuse. You're right that modern computing is full of DRM, but unlike a computer, an Xbox is literally just a DRM box. They rely on their hardware DRM to prevent piracy.
Not sure if it's still the case but back in the day, people would install aftermarket disc readers in early 360s specifically to allow it to play unprotected game discs, so anyone with a DVD burner could burn a pirated ISO onto a disc for their Xbox