Might be because people are running the headlights as Daytime Running Lights when the vehicle is not equipped with DRLs.
If DRLs are part of the OEM Body&Frame computer, they either use the turn signal lamps or they use the High Beams wired in Series (which means you are running 12V into a 24V lamp set, so it's half brightness, or less than half brightness, vs high beams and dimmer than low beams). DRLs are required to be relatively dim and the MVSS will limit the lumens they can project.
They use the High Beams because DRLs in nations that require them must aim straight ahead, which low beams aren't designed to do. Turn signal lamps can be used because Canada allows amber or white for DRLs (European, UK, Russian, Japanese etc don't. This was done as a concession to the Big3 automakers who wanted to minimize parts differences in North American vehicles).