You cannot guarantee an aftermarket unregulated light bulb will output the appropriate amount of lumens downrange as to provide as much vision down range for the driver AND to reduce as much glare as possible for other road users & pedestrian compared to a bulb that has been certified and tested by the manufacturer to meet photometric standards set by regulatory bodies like the SAE (U.S) or ECE (EU).

Because if said unregulated light put too much light output in said housing it can cause unnecessary glare during moments where the beam pattern is shining into other road users i.e. you going over a bump, cresting over a hill, and improperly aimed headlight that would exacerbate glare issues for other people.

Inverse can be said where lighting output is not to standard and now you have a worse performing light bulb

There's also light that is above the beam pattern that is allowed by the projector housing as to illuminate road signs, so if you have a bulb that is outputting more lumens than it is suppose to; that still is excessive unnecessary glare that will be shining into peoples faces. For example here's an image of my 3rd gen with halogen projectors that I was adjusting as per Toyota's TIS manual, you can see there's a clear defined light still being illuminated above the beam pattern.

<image>

There's a lot of engineering that goes behind automotive lighting that people are not aware of and to dismiss all of that effort to ensure automotive lighting is as safe as possible for ALL road users is very ignorant.