First of all, Star Wars invented the Event movie.
Prior to Star Wars, movies had to be in and out of theaters for Decades to make that kind of money.
Star Wars changed all that.
Now, nobody lined up on the first day, people just didn't do it back then, but after the first week, it was a certifiable phenoma.
But, at the same time, you can't blame Disney for missing the boat. Fox didn't think much of the project either that's why they gave Lucas so many of the rights. Lucas only made the film because of the success of American Grafitti. NOBODY in hollywood expected what it became.