You're entirely missing the point. If I'm spending a month to optimize some code so that it is 25% faster, these gains don't go away again once I'm done optimiz

You're entirely missing the point. If I'm spending a month to optimize some code so that it is 25% faster, these gains don't go away again once I'm done optimizing. They stay in the product for months or years. And this is where the effort pays off.