I sell these all day at work.
Aftermarket, the blame largely lies on the end user incorrectly selecting and fitted LED modules, but I still see this problem far too frequently with cars coming off the production line.
I cannot tell if it's the business incentives around the engineers designing these boards, an actual lack of understanding of optics from them, or a failure in due-diligence from companies they supply to.
As a person formerly heading down a physics career: LUX AND LUMENS ARE COMPLETELY DIFFERENT MEASUREMENTS!
I am worried far too many companies are taking Lumen readings from incandesent bulbs they are trying to replace, looking on DigiKey and selecting whatever COB from Cree with the same amount. This is not how it works physically and especially not how it works for how humans percieve light!
I wish more work would be put into the proper testing of the diffusion of light. Yes diffusers exist from proper companies like 3M and yes they are used, but it to me seems beyond something you can just dump on an otherwise busy engineering team in isolation and expect good results. You need proper user testing and more importantly need the cost of diffusing methods to come down many order of magnitude per mm^2.
And I'm not even covering other considerations like colour rendering index optically or standardisation of techniques compliance wise.
It is an emerging area, but I can't help but be aggravated by the seeming lack of process. Good LED specialists understand how to make them look correct, the rest of the world just can't seem to yet.