Because it takes hard work and discipline to objectively determine where to optimize or whether an optimization is necessary - let alone to determine which situ

Because it takes hard work and discipline to objectively determine where to optimize or whether an optimization is necessary - let alone to determine which situations need to be optimized for in the first place.[1] And, frankly, quite a bit of premature optimization takes less time than doing that work. [1] Optimizing for readability has definite pay-off over the life of a project, but good luck quantifying it ahead of time.