Basically because the show is obsessed with showing everything the books/movies only talked about it ruins the fantastical nature of it all. There is no imagination about the Mines of Moria (Khazad-dum), Numenor, the Elves before ditching Middle Earth, the Hobbits, Gandalf and even Sauron in RoP. The fantasy aspect is literally just all being shown so rather than being fantasy its just a general action drama that happens to take place in Middle Earth.

To add to this, the mystique and majesty you would assume of somewhere like Numenor and Khazad-dum are broken. Numenor looks like a generic port city of an island nation and Khazad-dum looks like any run of the mill idea of a Dwarven city. It takes away from how YOU imagined both of them and this can extend to Sauron, Celebrimbor, Isildur, Elrod, Gil-galad and even the pre-Hobbits.

There is no mystery to uncover, we all know it already. There is nothing interesting happening cause we literally know everything that happens. We know that Khazad-dum gets destroyed, we know that the Elves leave, we know Sauron wins temporarily, we know Numenor gets annihilated, we know Isildur falls prey to the ring, we know Elrond and Galadriel are big players in everything. The books and movies provided this information without ruining the fantasy by simply saying it happened rather than going into immense detail, leaving you to wonder. RoP wants to tell you what happened while not even using foreshadowing effectively. The actors are doing great (Durin and Elrond's relationship is an enjoyable part of the show) but the writing doesnt know what he wants this show to be.

Ok, define fantasy in the context of a show of movie.