Love your pony art...
Sweetie Belle: "Rarity, you hurt Growlie's feelings!" >: (
You don't do that normally do you?
There is a difference between making your own interpretation of the copyrighted content (that is, e.g. fan-art, fan-fiction) and putting the exact copyrighted content (intellectual property) into something else without permission (or even worse, monetising it).
In my opinion the game used too many original, copyrighted resources which could make the game look like it has connections with Hasbro. This could put a bad image on the franchise and cause some legal trouble. All a parent needs to know that their beloved ones are playing a violent fighting game with cute little ponies, which suppose not to fight in the first place. So, for such a game to exist, it would definitely need a "T" rating and obviously a licence.
All I'm trying to say is that it was a mildly brutal fighting game based on a show which targets little children. It would be available for anyone without restrictions, which as a result could be detrimental for younger players, Hasbro, and maybe for the whole fandom itself.
There are many MLP games here on DA and I don't see them being taken down. Even original animations or PMVs seem to not bother Hasbro. They do know about those videos, games, comics... so why only Fighting Is Magic?