(I'll assume you're not joking, because your post is ridiculous enough to look like sarcasm.)
The answer is because programmers read code 10 times more (and think about code 100 times more) than they write it.
How many times have you read a story card and by the time you finished reading it you thought "It's an easy task, should take me 1 hour of work to write the code and tests"?
In my experience, in most of those cases the AI can do the same amount of code writing in under 10 minutes, leaving me the other 50 minutes to review the code, make/ask for any necessary adjustments, and move on to another task.
My ability to review and understand intent behind code isn't a primarily bottleneck to me actually efficiently reviewing code when it's requested of me, the primary bottleneck is being notified at the right time that I have a waiting request to review code.
If compilers were never a bottleneck, why would we ever try to make them faster? If build tools were never a bottleneck, why would we ever optimize those? These are all just some of the things that can stand between the identification of a problem and producing a solution for it.