I believe it is going to be immensely popular in Japan to where it will make the opening of Diagon Alley look like child's play. But I don't believe it will have near the popularity in the US. I think it will be a popular land in terms of merch sales, rides, customer satisfaction and everything that is great about a land- I just don't believe it will be an
Attendence driver like they might think it will be.
That won't necessarily be a bad thing though. If overall spend and satisfaction goes up, like I believe it will be- it's a win.
So to answer your question- Why? No clue. I guess my gut? It's just an opinion based on feeling and no stats to back it up- so it's literally a useless opinion. Hah.