Uhm so they can fit more fans in the building is one of the reasons.
More room for seats
Thank you guys, it makes sense to fit more seats in, I just didn't know
More seriously, you wonder why the NHL hasn't considered going to a bigger ice surface. They're trying to minimize the head injuries and take the goons out of the game. That would help. I know there is more to it, but you never really hear it brought up.