Lucas's problem has largely been that Star Wars is an object he crafted that took on a life of his own while he lost interest. He saw too much of how the sausage was made to get caught up in the illusion and to him he just sees the technical application of film making tricks. When he returned to make more films decades later, he was returning to a universe that people had put far more thought into than he had ever intended and the prequels were made without really absorbing what the universe had become in his absence.
They're still kind of technically disastrous films, with confused storytelling and frustrated actors trying to work in a green void, but the big difference between I and VII is how much the creators of those films were invested in the fictional universe as a whole.