Right, but presumably the Doom and Quake server code was written by id Technologies themselves. That's not the case with a lot of modern multiplayer games. They

Right, but presumably the Doom and Quake server code was written by id Technologies themselves. That's not the case with a lot of modern multiplayer games. They license middleware like Photon Engine and don't have the rights to redistribute the server software, even in binary format. I guess they could just strip our the parts of the server code that they don't have the rights to redistribute, but then it wouldn't be functional.