Because Zelda has a more charming tone, Horizon is a world in ruins and those particular enviroments are brown which is obviously not as appealing as a green place with sun shining on the flowers.
You can see that there is a lot of detail put into Horizon (those gifs show it). It's technicaly obvious that Horizon looks better, some people just prefer a different tone that Zelda provides.
Horizon feels one good generation ahead but it doesn't mean it will be a better game
I really like the latest Zelda Trailers but the graphics are partially killing my hype