For the same reason that there's no reason to think AI will continue to advance exponentially.

The idea of the singularity is fun, but it's unrealistic. Nothing lasts exponentially forever.

Even if the exponential improvements, which have been happening in both hardware and AI algorithms, were to slow down to sub-exponential, this still assumes that exponential advancements are necessary for AI to reach a level where it can assist in algorithm design. And only now we're seeing big jumps in AI investments, which could serve as another source of improvements. You could even argue that we're seeing the first signs of recursive improvements, with Copilot making programmers ~20% more productive.