Therein lies the inherent problem with the MH franchise and Capcom in general. They are not a console manufacturer, they do not gain the most benefit from having their games sell consoles (which is a flawed economic philosophy btw, "games sell consoles" doesn't explain why the dreamcast died for example).
I actually am familiar with the series, and because of that I can recognize that until Monster Hunter X, the series has been extremely dull, un-innovative and stagnant. MH3 had the new water thing which failed, and was removed. MH4 added mounting... which is honestly a mess, but at least it was newish. A couple new weapons each time, but ultimately rinse/repeat. Monster Hunter over the years has given me more of a feeling of Super Monster Hunter, Super Monster Hunter Arcade Edition, Super Monster Hunter Arcade TURBO.
FORTUNATELY for all of us, Toukiden and a few other series have started popping up in the genre. This means competition, this means Capcom actually needing to breathe a LOT of life back into this series, instead of their usual minor updates between releases. This means that -potentially- they could be forced into the Vita environment, unless they want to just give up that entire Japanese market. Maybe they will even push the game to a point where the things they want to do with it are too limited by the 3DS and they will HAVE to switch.
But keep in mind, they are not going to look at hypothetical. They are not going to hope that releasing a Vita MH stateside will push up Vita sales. They are going to look at numbers that already exist. About 20% of people who bought a 3DS in 2015 picked up MH4U. If 20% of people who bought a Vita in the US that same year bought a MH Vita game, they would only sell around 46,000 copies.
I don't want to sound like I don't want MH to succeed, or I don't want it to come out on something other than 3DS, I absolutely do. Just not like it is now. If MHGen were to get ported to Vita, it would fail, and Capcom would give up on ever moving it out of the 3DS ever again. It needs, really deserves, a full revamping and overhaul to make it succeed on more powerful systems. So I think, oddly enough, the best way we can help Capcom and MH get there is to buy a copy of Toukiden 2 when it comes out because if that game fails, and there is no more competition to MH, you better believe you will never see a non 3DS MH game again.