It's nice in theory, but in practice many (most?) games are using middleware they don't have the rights to redistribute as open source. IIRC when the source code for Doom, the first major commercial game that went open source, originally came out, it had all of the sound code removed because it was dependent on a third party library. Not that you're going to have sound code in a server, but you may be using third party libraries for networking, replays, anti-cheat, etc.