diop With tech products that are basically commodities like laptops, screens, and phones, there is very little testing. These things are built for specs. The company that sells them, the suppliers, the assemblers, all buy parts based on specs. A few prototypes are sent out but mainly to see the form factor.
A perfect example is the recent Macbook Pro and their keyboards. Nobody liked the keyboards and found them impossible to use. This shows nobody really tested the product beyond just inspecting how it looked and the specs. Same with the new Samsung phone that folds. There was no testing done on that.
As far as the response from companies, this is a little different case as it's a specific set of medical symptoms caused by a specific type of product. It also appears that using the screens for these users causes problems in other aspects of life that they had no issues with before and the effects can last for months, years, or maybe for life.
However, I believe several companies already know about this issue. That's why newer screens have "eye care" settings and they are adding the f.lux type filters to all devices. They know there is a problem but there is little incentive for them to investigate it. They make money by offering new screens with better specifications, not by fixing their old screens. The market just wants to hear higher numbers, like higher resolutions or more colors. So the makers of these screens are using any techniques they can to reach these specification and eye strain isn't even on the list of things they care about, even though it should probably be first on the list. Phones, laptops, and screens are sold based on the specs they have and how they look at first glance.
If they were forced to address the problem under threat of liability, they could probably find the culprit within a month or two.