I think we can all agree that Kingdom of the Crystal Skull was an underbaked idea. Something that most of us would rather pretend never existed (much like the Star Wars prequels). This banter explains the whole situation:

George: Let's do aliens.
Steven: I don't wanna do aliens.

Years later...

George: Maybe you're right. We shouldn't do aliens.
Steven: George, I love ya!
George: We should do inter-dimensional beings.
Steven: What?!
George: Yeah, ever heard of string theory? They're from another dimension.
Steven: Fine! Fine... What do they look like?
George: They look like aliens.
Steven: facepalm

Moral of the story - George Lucas is a genius filmmaker - but he needs people around him that will reign him in. Heck even Star Wars: A New Hope was saved in the cutting room. If you watch some of the dialog and scenes that were cut or pre-editing - they were just painful. Utter crap.

Let’s hope with The Dial of Destiny - George had some really good people around him that held him in check.