I’ll never be able to find the direct quote but Lucas wanted the original Star Wars to feel like it was beginning ‘part way through’ a story.

This mentality of under-explaining rather than over-explaining has persisted (Snoke) and it definitely wont be something that Lucasfilm would likely ever want to change.

Why?

Because it gives them loads of creative leeway to later “fill in the blanks”. With prequels, sequels, stand alones, TV shows, video games, books, comics, etc. It’s genius.