Because if OP is on then if someone attacks your base you log off the attacker gets pissed off and spawns 5 bases around yours and loads it full of ammo then you log on and get destroyed and then post a complaint on forums and then it gets removed 
Here is the story: A Real Low Blow
Besides CV’s Can’t use their main guns on planets so bases are a hell of a lot stronger now than they ever where, I for one will be building on planet :]