Lucas was also disgusted with moviemaking politics. He’s an interesting guy—he started out as a guy who wanted to make art films, then Star Wars hit. He grew tired of directing after the first one—he’s not a people person and reportedly treated his effects team terribly and people did not like him. Indiana Jones was his concept but he felt like Spielberg got all the credit. Other stuff he produced, like Howard the Duck and Willow, were poorly received. He withdrew from moviemaking, devoted himself to the sound and VFX stuff, remained in the Bay Area.
He and Coppola started out together as friends and collaborators and had big dreams to exist outside of the studio system, but only Lucas got that power and he was tethered to Star Wars. I think it just took him a long time to come to grips with it.
My question would not be why he didn’t make more Star Wars films, but why he didn’t turn to more artsy and/or personal films like he started and originally intended, but the answer to that question is probably in my first paragraph up there.