No guilds = FAIL.
Guilds offer entertainment and camaraderie that the game alone can not produce. Replayability is the essence of any game... and guilds specialize in this. It should be of tremendous value to Larian.
I see this as a major oversight.
If you want to start a guild that is up to you, not Larian. This is not an MMORPG, so it's definitely not a fail from Larians side to not implement something like that. This is as much an SP game as it is MP.