That's always been the issue IMO.
A fantasy world game setting accessible enough to attract a lot of gamers is really generic. D&D is derivative of LOTR, Conan, and all the other stuff that people are bought into.
The best fantasy movies with original settings are weird. Labrynth, Pan's Labrynth, Princess Bride, Neverending Story, Time Bandits.
The ones with 'generic' fantasy, like Ladyhawke, Dragonslayer, Legend, etc. have aged really poorly. They're not memorable. they're being left behind.
A 'real' D&D movie is a very odd beast. Other than Stranger Things, I'm not sure how it would ever translate.
Like I posted before, I feel like an early Peter Jackson or Gilliam-flavored absurd gory murderhobo comedy would do it justice, but it couldn't get made.