Denuvo is a digitial rights management (DRM) tool used by game developers to ensure that their game can only be played by legitimate users. It operates by constantly communicating with a server that validates your log in info. Since it is extremely difficult to remove from the game, it is normally gotten around by setting up a spoofed server that the game can talk to instead.

The issue is that this communication takes resources and clock cycles from the user. That means that by implementing denuvo into your game, you are actively slowing it down. Whereas on the spoofed server, that is a local server(meaning it's on the same machine running the game) so they can communicate much more rapidly, basically instantly.

Tl;dr by implementing denuvo you are ensuring that pirates have a better version of the game than your legitimate users, thereby driving otherwise legit users to piracy.