I found an interview with Baz Lurhann, where he states that he wasn't interested in doing a straight bio-pic but loved the idea of taking a historical figure to explore a bigger idea. So he used him to explore "where we are right now" with all the lies and half-truths, and manipulation.

He didn't care if he got the story right - he was exploring the idea that Elvis represented. That's how you do a biopic or make it interesting.

https://www.youtube.com/watch?v=CPcwWeJ92VE

Austin Butler - also was most interested in hunting who Elvis was behind all the talent. What motivated him and made him human.