Because it's obvious marketing BS to predict exponential growth?

Exponential growth is a rare phenomenon in any area, let alone computing or industry. To predict it will take place without hard data that it's already happening or a perfect analogous reference, is not possible. You've been deceived.

All that's happened is a new tech has reach MVP maturity, been released to the masses, and now it's plateauing in terms of raw power increases, whilst continuing to mature in terms of applications.

AI power output will now proceed at below Moore's Law levels, because it's mostly hardware bound. Applications will jump around as we saturate our lives with more and more AI-enabled devices.

None of that is exponential. How could it ever be?