It might also be because Lucas is from an Indy film background, which are traditionally low-budget and require the filmmakers to think around problems creatively. Even when he was working on American Graffiti for Universal, elements of his background showed up. That film had a small budget, and he filmed it in less than a month. And Star Wars had a modest budget as well. So while neither of those films were independent films, he had to work under similar Indy constraints. So it's rather ironic that now that his films are independent again, what he makes seems less and less so.

To refute my own theory, though, control is also a huge element of being an Indy filmmaker. You can do whatever you want to and are in control of most aspects of production. And we all know the hassles he had on Star Wars at not being able to control certain elements he was used to controlling. So now he is back to independent films and is able to control everything again.