Also I think Luca$h's close relationship with Francis Ford Coppola during the 70s is telling. This is the period of 'The Godfather', 'The Conversation', 'The Godfather: Part II' and 'Apocalypse Now'. I think the serious-mindedness of his friend's very successful filmmaking output at that time may have rubbed off on him.
There is a shift generally, from 70s to 80s American blockbusters, from a big adult audience to a big youth audience.
What came first, the chicken or the egg? It was the egg laid by the chicken's evolutionary ancestor.
Spielberg and Luca$h practically invented the summer blockbuster in the 70s and what audience is around in summer that ain't there during term-time? Kids. Crowds of 'em looking for a thrill. The film companies decided that if they tailored the films to the "youth market" they would out-compete anything else around. Unfortunately they've given kids less and less credit as time has gone on.
Luca$h actually thinks more kids will enjoy his films if they know how the Force works, so he introduces midiclorians! He thinks that they won't understand it when Darth Vader (in ESB) says: "bring my shuttle" when he's in Cloud City and then appears on a Star Destroyer, so he adds clumsy extra dialogue to explain it. He thinks that they won't be able to cope with Han Solo being a hero and also gunning down an alien, so he changes the scene to a worse shot with awkward CGI alterations just to make the alien shoot first. He doesn't think kids can understand metaphor, complex personalities, character development and he also thinks your little sister can't cope without something cute and/or stupid (Ewoks/Jar Jar) to keep them interested.
He gives his audience less and less credit as time goes on.