Because that more than what all six of these cost combined? Why do companies ever do remasters instead of AAA remakes? Square Enix is already actively developing four 2D-HD games. They aren't going to go suddenly 100% all-in on high-budget remakes, they have to balance remasters, remakes, and genuinely new games.
FF1 is already getting a high-budget reimagining (Final Fantasy Origin), and I suspect FF6 will eventually get something higher budget at some point. But Square Enix has a ton of games in the pipeline at the moment to the point where it is hard to imagine there being appetite for tacking on a few more $10M-$20M remakes. The 11 "announced" remasters/remakes/reimagining, + FF16, Triangle Strategy, new SaGa, new Octopath, new Mana, new Taro game, and that's just from the JP side of things.
It all depends whether these are from the ground up, or ports of a specific version with overhauld graphics engine. We really don't know enough to say.
There is no chance After Years is part of the initial $15 release.
Nothing about the PSP release grabbed me. DS version or bust. I think I'm going to find it extremely difficult to recommend the PR version over the existing Mobile/PC release for it.