Even if flying cars were cheap and easy to make, would we want them? They're cool and amazing, but in real life they might be impractical.

So generally when talking about the future, maybe we predict inventions that make for cool easily understandable stories, instead useful or plausible inventions. That's why flying cars were predicted but the internet wasn't.

If you're not even going to be alive when the time of your prediction comes, why would you bother to think hard about it and make an odd, abstract, unfashionable prediction instead of a cool story about flying cars?