You're forgetting the fact that Freedom Unite came out four years into the PSP's life meaning that Capcom wouldn't be able to match those sales on either device. When compared to the other MH games that came out earlier the new one is progressing pretty well so while it probably will come to the Vita eventually its not going to be from a lack of sales.
also, judging from what I know about the rumor I wouldn't get my hopes up.
From: KGTrigger | #002
I would honestly prefer a Phantasy Star game. Hey, there's already one announced, isn't there!
I'm pretty sure there isn't unless you count phantasy star online 2 which is coming to the PC
there was a rumor about a game coming to the Vita but there is no evidence really supporting whether its coming to the Vita
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