Some things to consider.
1) Zelda is not a wildly popular brand. BotW is wildly popular, but Zelda is not. People did not buy Skyward Sword or Link's Awakening on the Switch like they bought BotW. Age of Calamity sold really well for a Warriors game, but it likewise did not put up numbers like BotW. BotW has some really amazing sales and legs, but that is not translating into sales for other Zelda/Hyrule titles.
2) The title, i.e. the branding, for TotK is terrible. How is a casual gamer supposed to know that this game is like BotW? I.e. a casual gamer is someone who doesn't go to internet forums or social media to talk about gaming or look at gaming videos. They look at the box cover and talk to friends. Box art like BotW is not enough, because you can look at Age of Calamity sales to see that box art is not enough. The Zelda name is not enough either, e.g. Skyward Sword. This game needs "Breath of the Wild" somewhere in the title or something like it.
3) The gameplay is going to be disappointing for a lot of people. I can tell this, because they aren't really showing off the gameplay. Recall E3 2016 when Nintendo was the punching bag for the gaming press and internet gaming culture. They come in and show off basically one game: Breath of the Wild, and they show off hours of gameplay. They also say, "Hey this is just the starting plateau and there is tons more left to show." They knew they had something great and they wanted to show it off. They aren't showing off this game. They don't seem to have faith in it.
Given, there are also a lot of people out there who are highly anticipating the sequel to BotW. That is why I think TotK is going to sell well initially. But once the most enthusiastic BotW fans have bought the game, legs are not going to be like BotW. Legs are going to be disappointing.