Quake II is literally not the same as an MMO. You have a small map with a maximum of, what, 32 players? MMOs can have thousands. Most modern MMOs can handle hundreds in the same zone before they become unplayably laggy. Most can't handle thousands in one zone, even on the machines the servers were built for. You can't do that as a consumer.
It's not about the code. It's about the game itself and its requirements.
Emulating servers doesn't change that.
Again, it's all about being able to connect everyone that is playing and the difficult parts being managed for you. You never have to worry about spinning up a dedicated server to play with your friends. You just load in, invite them to party, and queue up. These conveniences are why this model is popular, not because of this bizarre conspiracy you're pushing.