They do it because they get saftey ratings which are occupant based.

You want the absolutely brightest, longest shining lights possible to light up as much of the road as possible, but that has consequences for others.

Theyre probably bumping up against whatever high end limits are allowed before the saftey agencies cause a fuss.

But while it might solve one problem fixing this issue, it will probably cause another, e.g more people will be overdriving their lights.