Well, it needs electricity. For most of history, we didn't have electricity. And, we didn't have cheap electricity until electromagnetism was understood and electric power could be made from rotating machinery. After that, there needed to be found a chemistry that would allow aluminum to be made directly, rather than from sodium or potassium reducing aluminum compounds.
The actual physical amount of energy needed to make aluminum would have been available since forever; it's the form of that energy that wasn't there.