A lot of gamers (casual and hardcore) played this in 1997, and a lot of those gamers who fell off gaming as they got older are back to play this. I've mentioned this before in other threads but my boss, for example, is 42, and bought a PS4 Pro for this. I was the one who told him it was only the Midgar section. The disappointment was palpable, he went through the five steps of grief in real time right in front of me.
For the record, expanding on the Midgar section of the game and releasing it in parts is fine to me, they just need to effectively communicate that change to prevent disappointment from misinformed customers, and so far, I don't think they have made a reasonable effort to do that.
I also believe if they don't make a reasonable effort to notify customers that this is not the entire FFVII experience, someone is going to try to sue them and while it won't result in damages being awarded, it will result in legal fees and bad PR for Square Enix.