Semiconductor density, speed, and power efficiency grow much slower than doubling every six months. Creating custom silicon for this won't help - plenty of companies, including Nvidia, are already optimizing their hardware for these tasks and they are very good at it. Production capacity can't scale nearly that fast for myriad reasons, including access to materials, production capacity of inputs, the time and complexity of building new production facilities, the lack of experts available for all of this, and the long time frames for training new people.
This to me is the biggest sign that this is a bubble. Even if demand shrinks, it could still be huge. Even if many use cases are impractical, we will still find some where it's valuable. But the market is basing its valuations on forecasts of tremendous growth that simply can't be supported physically.