There is a really really bright light shining on them against a background dominated by well not much, the glow of the milky way.

Consider our moon is the one of the darkest objects we know of, about the color of a asphalt parking lot.

Via Wikipedia: "The Moon has an exceptionally low albedo, giving it a reflectance that is slightly brighter than that of worn asphalt." Yet, the sun is /so bright/ that even at 380,000km we see moon-shadows at night on earth.

To a first approximation, small LEO satellites are roughly the same angular size as Venus at its average distance to us.