vivec killed nerevar to make way for his rebirth. he killed morrowind for the same reason. that and he is a self-centered little fellar.
But the thing is there was no need for him to destroy Morrowind, because he could just snap his fingers and Morrowind would have been reborn. In an infinite perspective there is no need for anything to happen, because it is pointless.
The main reason I don't like this view of CHIM is because I think it's horrible lore. It's like the old "if god can do everything, why doesn't he help everyone" and so on, but in this case the answer is "he doesn't feel like it". What kind of a [censored] answer is that?
The way I want it to be, is that when one has achieved CHIM, one knows everything in one's own mind, and if one keeps meditating or whatever, it happens as MK said, the world you've created in your head becomes a new universe where you are the godhead. But before one becomes the godhead of one's own universe, there must be a phase where one is seemingly cut of from the world one existed in before, and noone can properly interact with you because they can't see your dream. That would make more sense, or at least I think so.