Oh I don’t disagree that location and culture figure into it. Tolkien was a linguist who was fascinated by ancient languages, so it’s not super surprising his dialogue is very old fashioned.

However, that 20 year difference is a big gap in terms of entertainment and modern story telling sensibilities. Tolkien grew up with silent films, by the time he’s in his 50s, Hollywood is just starting to develop the visual storytelling we’re familiar with today and move away from more theatrical and presentational performances and become more realistic.

Compare that to the media Herbert grew up with, and you’ll see a stark difference in how the west adopted storytelling sensibilities. The influence of Checkov and how western audiences gravitated towards realism really gets cemented by the middle half of the 20th century.

The same jump in storytelling styles happened in writing as well. By the 60s we’re seeing stories that also really start to focus on realism in regards to dialogue. Especially in sci-fi. Fantasy tended to be more stylized. And maybe that’s in part because Tolkien set the bar, and because fantasy tended to be about creating modern myths, whereas sci-fi tended to be about exploring ideas that humanity was dealing with in that moment (or obsessing about).

So long story short: I agree that there are many factors that influence writing style. But also a 20 year gap in the time those writers were active saw a massive amount of change in how people wrote stories. Media was taking large leaps forward. And while I do think Dune is more modern in its Prose, it does still feel somewhat dated, but not nearly so much as Tolkien.