^I deserved that.
But seriously, you have to remember the decision was not Capcoms alone. Nintendo also had a hand in it and historically Nintendo is shy around a lot of online things. Though you are correct in MK7 having a lot of online support the online interaction it provides is still a lot less than what you would see in a game such as MH. In MH you have player to player interactions, talking, you have the monster data, and a lot more. In MK7 how much interactis there really between the players?
And thats where Nintendo gets shy... even on the 3DS streetpass nintendo has many words and phrases blocked. on mario Kart you cant interact aside from racing. With MH3G nintendo cant really stop people from saying things to each other if they are beside each other but by not adding online they can add that level of safety. SO in my opinion I do not think in the development of 3G it was all Capcom's decision to not add online but a big influence from Nintendo as well.