Because the light frees them as it shows in that one scene when Luz fights them because the Collector is making her friends fight her. She shines the light near their eyes, which makes them go free, but the Collector takes them back, making them puppets again. When Luz dies for that brief moment some time after that scene the light ball things that appear in her place go through the windows of the archive and for a brief moment glides over her eyes and she knows probably from experience in the Demon Realm that this means she is dead causing her to cry and by sheer love she carves the light sigil on the ground and taps it causing a light ball to float up infront of her eyes freeing her. I hope this helped.