I think the problem starts on the MH portable 3rd on PSP, here's some quote from some ppl from 3DS board:
"And Sony basically almost canned the localization of it here in the West because they wanted to change the AdHoc Party and make it more "Sony Friendly" with Achievements and Trophys and have it make use of PSN, etc. etc. Long story short Sony wanted to make a bunch of changes Capcom didnt like"
"From what I recall, you have it backwards. MHP3rd used some sort of network feature in JP that NA didn't have, and for Capcom to localize it, Sony's NA network MUST support it. Needless to say Sony of America did not take to it kindly. I don't blame them though, who would change an entire infrastructure just to accommodate a single game, even if it is a monster of a game?"
Hmm....2 conflicting statements there. but I think the correct one is the first, because looking at the current 3DS release, it doesnt even have any network support or online play. it retains a local wireless play similar to MHFU.
Anyway, Sony really stuffed up badly by losing MH franchise. and look at the sales of 3DS in Japan Now! last gen, PSP did very very well in Japan, but now VITA sells so poorly.