The late 70s, again in the late 80s. See wikipedia.

https://en.wikipedia.org/wiki/AI_winter

Yeah and if you look at the blocking factors at that time (data, compute) these type of limits currently are non existend.

There is a difference to be acknowledged: in the 70s/80s the whole world didn't suddenly start to shift to AI right?

So why do so many smart and/or rich people push this? Hype? Yeah sure but hype was here for crypto too.

I bet its an undelying understanding and the right time with the right components: Massive capital for playing this game long enough to see through the required initial investment, internet for fast data sharing, massive compute for the amount of data and compute you need, real live business relevant results (it already disrupts jobs) etc.