Are you sure that's true?

New vehicles from the factory (obviously 50-state DOT approved) are available with fog lights that operate at the same time as low beam = total 4+ bulbs on simultaneously. My understanding is that the legal limit is wattage (which is why wallyworld & your local parts store sell only the 65w/45w 9004 bulbs and 65w/55w 9007 bulbs. You'll notice that anything at either of those places in excess of those wattages is labeled "for offroad use only".
However, your point is well taken that the reflector behind the bulb pair toward the center of the vehicle (9004 bulb in the sportlights) is focused more for high-beam driving lights and would be more obnoxious to oncoming drivers if also illuminated on low beams.

I wouldn't be surprised if there were any legalities involved that it was this aiming/projection that would be the concern rather than the number of bulb elements that were energized. (And on those grounds, I'm going to make a small revision to my wiring harnesses to take the 9004 low beam element off the low beam circuit and add it to the high beam circuit. )
Thanks for bringing this up.