FF15 sold 5 million copies on the first day, while FF16 took a few days to get to 3 million. It’s not selling as well as 15. Anecdotally I’m seeing far less discussion of it online than when 15 came out.
They also have more competition this year. Personally I won’t get it till it’s on sale because I haven’t enjoyed a FF game much in a long time, so I don’t really trust them anymore even if critic reviews are positive.