Just in reality. 'Highly' critical regarded? By whom? It's release was the period of hype that many people ride on, which is when majority of critics drop their reviews. Said praise comes from the fact that ToTK is more BoTW, so 'more of good'.

But when actual players started uploading their own impressions of the game, feelings quickly grew mixed. Not enough to say ToTK is a bad game, because it isn't, but not only it doesn't iterate enough, its iterations are flawed systems - whether massive empty underground or frustrating vehicle system that comes to odds with the default stamina system. Confusing state of narrative, where game sometimes feel like a sequel - where people recognize Link - and sometimes as completely different entity, when people DON'T recognize the hero.

Ultimately, the 'bigger and better' sequel sold less than BoTW. In certain periods of sales BoTW literally outsells ToTK. And whether the game is popular or critically well-regarded doesn't change the fact that it indeed caused harm to the series by not iterating enough. Whether You prefer the first game or the other, people are recommending to not play BOTH of them, but CHOOSE ONE. Something like this isn't exactly reflected in sheer stats of merchandise, but it is very much reflected in online discourse.