Exponential improvements aren't very helpful if you're working on exponentially hard problems.

Exponential growth of technology hasn't solved machine intelligence (by direct simulation) for essentially the same reason why it hasn't solved numerical weather prediction or made quantum computers pointless.

To expand on weather prediction: you need an order of magnitude improvement in computer speed to make weather forecasts with the same quality one day earlier. So exponential growth of computing power means linear growth in terms of subjective benefit.

To be fair, we don't understand the difficulty of modeling intelligence anywhere near as well as we understand the difficulty of modeling the weather. But, given the limits of our current abilities to simulate the brain, it seems reasonable to guess that similar principles could hold.