Honestly, when you look at this from Disney's perspective, it doesn't seem like they had much choice but to do this. Putting Frozen in MK right now would only put further stress on the capacity balance issues plaguing WDW at the moment. MK is already the most popular park and I can't imagine adding a themed Frozen area there right now would be a wise move.
DHS is already getting a makeover and I am not sure they could put Frozen there anyhow with the rumors of Pixar and SW IP's going into DHS. AK is out of the question, so you have EPCOT, which is is desperate need of some love. The dilemma Disney faces is this, they can fix all the parks by adding new attractions and capacity then plan WAAAAAY down the road for a Frozen land somewhere in MK (which could still happen someday) OR they can use the ONLY place in EPCOT where adding a Frozen IP would make any sense (even if it's thematically out of place to begin with at EPCOT) and put it where Norway is since there is already a connection with the Film to Norway.
This will bring a lot of people to EPCOT and alleviate some of those issues with the crowds at MK. It adds something to a park that, honestly needs way more than this, but will take anything at this point and with Disney's, currently, strongest IP it is sure to attract crowds while the other parks get renovated/enhanced. Hopefully down the road EPCOT will see a lot more investment on a large scale, but the way I see it, Disney did not have a lot of options for Frozen.
Anyhow this is just my logical reasoning. I might be way off base....