(apparently mandatory-nowadays disclaimer that this is speculation on my part)



Even if the change of functionality between VII PS4 and IX hypothetical-Vita in that boosters disable trophies was a deliberate change, I don't see a mistake like labeling them as achievements rather than trophies as something that would have survived the earliest testing passes.



Hence it is my speculation that for whatever reason the plans for a Vita version were canned relatively early on in development, with code like that being vestigial leftovers.



(Also for what it's worth, Unity games on Vita don't have a stellar performance track record)