"AI hasn't been done yet because no one's actually tried."

Researchers have been trying to create some kind of framework for general intelligence since the 1950s with multiple governments (notably the US, EU and Japanese) throwing billions at it, with relatively little results - resulting in things like the great AI Winter.

We have lots of clever focused systems now that are made feasible by the enormous capacity of modern hardware, but I'm not convinced that we have made much fundamental progress on real human level general intelligence.

Note that I do think that general AI is possible - it's what motivated me to get postgrad AI research, I just think that it is a long way off. YMMV.