There's a pretty good take about how the thing that made Harry Potter the big superfad was the marketability, that you can show circular glasses and a lightning-bolt and everyone gets it. (Here we go! Verilybitchie on YouTube)

This is the thing that got Warner on board and willing to invest millions (in late 1990s dollars) to start not just the movie, but the sequels.

While Rowling's conservative values become evident in the movie (behaviors done by antagonists to show they're baddos is condoned when done by protagonists, elf slavery is good, etc.) is sometimes forgiven in other series when the author doesn't use their gains to support scary fascist movements that want to genocide people.