The Kingdom Hearts franchise is scattered among several consoles: ps2, GBA, psp, DS and 3DS. Because of that, it's probable that only some diehard fans have played all the games in the franchise. With that in mind, it makes complete sense to develop two HD collections, featuring 6 out of 7 games in the franchise. What makes piss poor sense is to make said collections exclusive to one platform. it's completely counter productive to the basic idea of allowing several people who couldn't play all the titles to do so. it's even a great option to bring new fans but the potential get's wasted.
The correct move would be releasing 1.5 and 2.5 on both Wii U, xbox 360 and ps3, allowing the biggest possible audience to play those six games and get ready for Kingdom Hearts 3.