The creation of package managers and the widespread availability of open-source repos means developers don't need to write as much from scratch.
The creation of search engines and Stack Overflow did (and still do) much of the useful things that people use AI for (boilerplate, debugging obscure error messages).
Machines have gotten exponentially faster for the last several decades. This means devs need to spend less time optimizing code. And the time to compile and run speeds up, meaning you can prototype things faster.
Why is it, that somehow none of these inarguable improvements to the speed and efficiency of development haven't lead to a a massive decrease in the number of developers? If we take it as axiomatic that AI significantly improves productivity, why, for the first time in history, does that not result in more programming jobs?