I chose to collapse the expanse but the mission that followed is for letting the ship explode. Why was a choice given if the outcome is the same?

ummm, do you understand voting? just because you picked one way doesn't mean you get that way. The majority voted the other way so that's the way it went.

I dont recall it being a vote, or saying it was a vote. I was under the impression that it was a choice and we would have a follow up mission reflecting our choice.

It was very clearly a vote. It probably makes little difference in the end, anyway.