Well, there's also the almost never mentioned Rock's Law:

https://en.wikipedia.org/wiki/Moore%27s_second_law

We do have flying cars, and we do have printers that print other printers, but both were some combination of really expensive/poor quality. Technically speaking, if you take it that most cities have 3D printers, most cities then do have micro factories, however that says nothing about general feasability...

Technology requires infrastructure and resources, and our infrastructure is strained and our resources are even more so... Until the costs become pocket change for the average person, technology will just remain generally unavailable.

> What does it mean to say "we were promised flying cars"...

I don't know about the other things you mentioned, but I think you have this in the wrong category. "We were promised flying cars" is one half of a construction contrasting utopian promises/hype with dystopian (or at lest underwhelming) outcomes. I think the most common version is:

> They promised us flying cars, instead we got 140 characters.

Translation: tech promised awesome things that would make our life better, but instead we actually got was stuff like the toxicity of social media.

IMHO, this insight is one of the reasons there's so much negativity around AI. People have been around the block enough to have good reason to question tech hype, and they're expecting the next thing to turn out as badly as social media did.