Hollywood was known to adapt a lot of movies from novels. A lot of the famous and Oscar winning movies were taken from books and were adaptations. So, the relationship between the literary industry and Hollywood was very close.
In the 90s, there were a few fantasy novels that got adapted into movies but hardly any of them worked because of high budgets and a lack of technology available for the filmmakers. It changed in the 2000s as technology improved by a lot and early superhero and fantasy movies showed the limits of fantasy stories on the big screen.
Fighting a dragon or jumping through buildings in a seamless motion was a cool thing to watch for everyone.
Though, it was still rare back then.
Any trend would get oversaturated with time and with technology only improving, more and more movies of similar type popped up. Some were original but majority of them were taken from novels as adapting a popular novel meant you already have a fan base.