I don't think they're truly blacking them out to the point that visibility for others becomes an issue; just making them darker; effectively dimmer.
While I like the look of window tint, haven't personally sought it out because I like to be able to see a pedestrian wearing black clothing, crossing behind a stopped vehicle, out the side of my window before making a left turn through a busy intersection, on a moonless night. Similar concerns over visibility of road debris and craters. In other words, I like to be able to look as much as possible, before I leap. Side window tint may to some degree, compromise that; and I have *very* good night vision.