Unlike a movie such as Suicide Squad — which did quite a bit of legwork familiarizing mainstream members of the audience with its core premise and ensemble — a Star Wars film maintains an accessible universe simply due to the fact that its so ingrained in our culture.
Disney seems to very clearly understand that it has something special on its hands with the Star Wars franchise.
Compared to most other major blockbuster film series, the Star Wars franchise has an incredibly timeless reputation, and it doesn’t necessarily require a thorough marketing campaign.