Wrong. FF7 was the second-best selling PSX game of all time, and is also the best-selling single-player Final Fantasy game. If you consider that remaking FF7 means getting the original fans PLUS introducing it to an entire generation of gamers who never played it on PSX then you would definitely expect it to sell.
If they didn't think a remake would sell then why did they literally call it "FF7 Remake" and not something else?