This isn't popular with the "everyone can learn to code" crowd but one significant barrier to becoming a proficient programmer is intelligence.

Maybe intelligence isn't the right word (after all how smart is it really to sit in front of a computer all day shuffling bits around?), a certain way of thinking or aptitude might be better. Education doesn't overcome this, training only partially overcomes this, experience doesn't necessarily overcome this. I bet most of us in the field have come across individuals with high levels of training, perhaps even very "intelligent" individuals who simply fail to fit concepts together in a useful way. Who get the pieces, who can answer quiz questions, who know facts and trivia, but simply cannot bring it all together into a useful, coherent, maintainable whole in a reasonable time frame. And I don't see this barrier being broken.

Anything that can be taught by rote memorization can be automated. Anything that requires higher levels of abstract thinking may never be automated.