1. The hardware isn't nVidia's primary moat. CUDA is. Currently all machine learning tooling assumes you have a CUDA device.
2. The hype cycle may be real, but nobody really knows how much better AI will become. The uncertainty is driving the hype (which is obviously on the optimistic side), but it could well be that models become so good that everyone "needs" an AI chip like how we "need" a smartphone today.
3. The gaming/graphics market is probably going to slowly shrink. There's only so many pixels you can push to the eye. There's very real diminishing returns there. At some point people literally won't be able to tell the difference between the newer/better/faster graphics and the older generation, at which point the GPU vendor's margins drop significantly.