This is an extreme version of adapting a small book like the Hobbit to a movie trilogy
I mean, the Hobbit is not the massive epic that LOTR is, but is an earlier work by Tolkien that is a children's storybook, and the studios who made the movies of the Hobbit decided to blow up the entire thing into a similar epic like the LOTR movies when there's simply not enough story to go around, and had to add things from the LOTR appendices, just for another moneymaker hit.
But Fantastic Beasts is WORSE, as it takes a small, fictional school textbook that was written by JK Rowling for charity, and has blown those up into (possibly) FIVE full-length movies, with all new content written by Rowling (who badly needs the cash, but can't write a screenplay to save her life). The movies have proven to be awful so far, and the only redeemable character is the Muggle baker, but since the textbook had no antagonist, Rowling had to fall back on Grindelwald, a lesser Dark Lord than Voldemort was, and what if Rowling undermines Harry Potter by making Grindelwald to me much more dangerous and potent than Voldemort? The two Dark Lords have already been compared to Hitler (yawn).
All in all, two shameless cashgrab movie series. Hobbit is poorly regarded, and so far, this is a well. Thank GOD.