So we track the kinds of things that we can measure and that we hope correlate with happiness, but we carefully check that they keep doing so. We shouldn't let one of them (like "maximize production") become the end goal itself!
Having a goal of 'maximising production' is the status quo - I am not proposing any changes.
I agree with you that the world would be a better place if our economy was focussed on achieving maximum global happiness, I just wanted to point out why it is easier to focus on an objective, numeric value like production than a subjective feeling like happiness (Gross National Happiness notwithstanding).