ROI might say a developer should build a different product instead of speeding up the old one. Or perhaps it’s better to get 200 less satisfied customers than make the 100 existing ones more satisfied. That can be done by using the resources for marketing, features, SEO. In the end, when you are optimizing there is always something you are not doing with that time.

Whether hundreds of users value the time they gain by not waiting for page loads isn’t relevant either unless it actually converts to more sales (or some other tangible metric like growth).