Theres no need for a campaign because what you expect to get is:
you destroy a capital ship---> cutscene
you capture a world------> cutscene
A world is captured through culture ----> cutscene
you die in your capital-ship---> Cutscene
More interaction can be in the from of an advisor speaking to you like how they do it in supreme commander. Otherwise its just cutscenes and voice overs.
I know it may sound good to others, its really not necessary because we write our own stories with every game we play.