One of the key reasons the Gellert Grindelwald (formerly played by Johnny Depp, now Mads Mikkelsen). Unfortunately for the studio, things have never fully got going for the series.
The first movie, Fantastic Beasts And Where To Find Them, was a solid enough success, with mostly positive reviews and a box office haul of $814 million, which was respectable even within the Harry Potter franchise. The broader problems ostensibly started in Fantastic Beasts: The Crimes Of Grindelwald, which was criticized by film critics and audiences alike and underperformed at the box office, making $654 million. There are myriad problems with Fantastic Beasts both behind-the-scenes and in of its approach to storytelling, but one of the biggest is a fundamental issue with the Wizarding World itself.
To varying degrees, all of the Fantastic Beasts movies, including Fantastic Beasts movies creating Harry Potter plot holes, this approach to worldbuilding also ignores much of what made Harry Potter feel so special to begin with: Hogwarts. The movies have touched upon the School of Witchcraft and Wizardry, most notably with the presence of a younger Albus Dumbledore (Jude Law), but it's never been the primary focus due to its titular storylines, and that explains in part why the franchise doesn't work as well as the Harry Potter movies.
It was Hogwarts that was key to making Harry Potter work. It was that location that so perfectly captured the series' innate sense of magic, both in the books and brilliantly brought to life in the movies (which weren't flawless, but did a great job of capturing the wonder of the school and perfectly cast Hogwarts' professors). It's in Hogwarts that Harry Potter offers the sense of escapism and acceptance that made it work its way into the hearts and minds of so many; where it brilliantly blended reality with fantasy to conjure up a fully-realized sense of place for readers and viewers to dream of going to. Fantastic Beasts is more of a globe-trotting adventure, which in turn means there's nothing to give it that same special feeling of place or to find that belonging.
This is in part an issue with even attempting to expand the Wizarding World, because unlike, say, Middle-earth or Westeros, the genius didn't lie in an expansive, richly detailed map full of different locations, but instead largely on a singular place that tapped into the joy of imagination, wish-fulfilment, and the childhood wonder that maybe this could really exist. The Harry Potter books and movies themselves went beyond Hogwarts with some great locations - Hogsmeade, Diagon Alley, the Burrow, to name but a few - but crucially they all, for the most part, served its Hogwarts-centric story in some way, be it a stop-gap on the way there or a brief pause amidst the term. They felt special because, in a way, they were an expansion of what made the school work, fitting into its core themes of friendship, family (biological and found), and acceptance.
The Fantastic Beasts movies tried to be bigger than Hogwarts, and thought they could achieve that by going to more locations and introducing a new raft of characters, before quickly adjusting course to fit more closely to Harry Potter's story - in particular Dumbledore and Grindelwald - but without re-capturing what made people love it to begin with and never truly being able to compete. Harry Potter itself gave hints of the larger Wizarding World that worked well - the Quidditch World Cup, and the presence of Beauxbatons and Durmstrang, all within the same book/movie - but they were always an addition to Hogwarts, never detracting from it. Of course, Hogwarts was Harry Potter's true home, which gave it an advantage over Fantastic Beasts' characters, but the likes of Newt and Dumbledore have obvious, deep ties to the school that it should pull on more to try and what made the series it spins off from so good.
