Let's take all facts into consideration.
Square Enix has a long history of planned Vita games that ended up being cancelled or released on other platforms instead.
Type-0 was planned for Vita but SE decided to go with home consoles instead. The New Dissidia was planned for Vita but SE decided to go the Arcade route. Nier port was planned for vita but the team that would work on the port had to work on Dragon Quest 10. Final Fantasy 11 was planned to be playable on Vita but SE decided to rather port it to Mobile's. Final Fantasy Agito+ is still planned to release on Vita but a bug in the Unity engine prevents SE from doing a lazy port so they won't do it. Square Enix also shared that they would love to HD Remaster FF12 in the future on both Vita and consoles.
Saying SE isn't supportive of the Vita simply isn't truth. They did port FFX and X-2 to Vita and actually the majority of the mainline FF series is playable on Vita. With SaGa we are getting a Vita exclusive SE game (although that probably will never leave Japan) and this year we saw the most SE vita announcements since a good amount of time. Dragon Quest Heroes 2 will also come out on Vita, Dragon Quest Builders will also come out on Vita and World of Final Fantasy is also coming out on Vita. Not only that but there is also a special edition FF14 themed PS Vita and Vita TV for all those who play FF14 through remote play.
So I wouldn't say that a KH game on Vita isn't impossible. people on the Vita subreddit would be even entirely happy with a simple port of KH1.5 / 2.5 on Vita.
And the Vita does sell decently enough to be considered a profitable marked. In the US the console is dead. Only around 2k Units are sold during one week. In Europe, mostly Spain, it's much more alive selling around 10k units and in Japan the average is 20k units per week.
And the whole nonsense about Sony no longer supporting it is not true either. Sony probably paid SE to also localize World of Final Fantasy on Vita. Sony also confirmed that they won't focus on big triple A exclusives for the Vita, for reasons said in the Extra Credits Video, but rather will focus on smaller multi-platform Cross play games like Helldivers. And Japanese devs will go to the Vita anyway because similar to the PSP many devs can't stand the 3DS's limitations.
Of course this isn't Ideal future for a console but at this point Sony isn't trying to make their console appealing the're trying not to loose their customers trust, which is something Nintendo isn't doing with the Wii U. I saw tons of people who got really mad and said they will boycott Sony because of how they mistreated the Vita.