I do get Rian’s approach, though.
While worldbuilding is an important part of writing any story, another school of writing would more emphasize themes - the why. What was the point of the story, and why did you need to tell it?
Worldbuilding is of course a great exercise in imagination and fleshes out your story, but it doesn’t necessarily justify your story’s existence on a deeper level. As someone who dabbled in film school, this is an attitude a lot of film academics and artsy professors push on you. Escapism and fun, is all well and good, but the best work is about something. While there’s only so many new ways you can combine tropes and derivative elements from thousands of years of storytelling, the unique experiences of different individuals in an ever-changing world will never run out.
Write not to make the most interesting, fleshed out worlds, or the coolest, most interesting characters - write a story with purpose and meaning to you, because everything has basically been done before. (And that can manifest in a multitude of different ways, not just plot.) That doesn’t exclude cool worlds and characters, but creativity from that perspective will naturally be more unique than just emulating what you like.
It was often explained to us as good practice because film is a two hour medium and you never know if you’ll get a sequel. Or the opportunity for an expanded universe. Moviemaking is a business, and your first pitches won’t spawn franchises without any proof of profit. And the studio wouldn’t need your hero’s journey in a sci-fi/fantasy world if they already have properties/options in that same niche. Without big names or money, it’s about making the Expanse when Star Trek exists.
This is definitely where Rian comes from. And it’s not something you can just unlearn. Especially when that’s how you begin to enjoy things. So when he gets the Star War, the question he feels he must answer with his film is “Why are there sequels?” from a thematic perspective. Not “How can I expand an existing universe?” If anything, the Star Wars world as already built on the back of at least 8 other films, hours of TV, tons of books, and so many comics - was a luxury for him. He just doubled down his film. He never considered it part of his job to curate anything more than those two hours.