That's their story and they're sticking to it
Square Enix has said time and time again that Crisis Core: Final Fantasy VII Reunion is a remaster and not a remake, but even they can admit that the lines are blurred a bit. That said, one area where Crisis Core: Final Fantasy VII Reunion won’t deviate from the source material too much is the story.
In an interview with IGN, producer Mariko Sato said that there are “no plans” to include any new elements in the story. There could still be some content added after the credits roll, but as far as the meat of the story goes, it’s going to remain true to the original game.
“Various improvements have been made to nearly all other scenes and battles, to a point where it could be said that the work we are doing is akin to creating a ‘remake.’ However, as the core elements such as the story are grounded in the original work, we call it a ‘remaster.’