George Lucas is the perfect example what happens when you don’t do world building.

If you get into those coffee table books about the making of the first three movies, you find lots of world building.

All the bounty hunters on the deck of Vader's Super Star Destroyer in Empire Strikes Back have canonical backstories, for instance. The cosmology of the galaxy - with Corusant at the center of the Empire and Tantoine way out in "Hutt Space" - was laid out by Lucas far in advance. "The Clone Wars" wasn't just an off-handed reference, it was a thing Lucas had defined as the WW2 precursor to New Hope's Vietnam. Hell, the fact that the first movie released was "Episode IV" should say it all.

One reason you got so many derivative works following Return of the Jedi is that Lucas dumped his director's notes to the public as merch when production initially stalled on the Prequels.