>>212125828
Because you need to actually consciously do it. Despite popular uninformed belief, kyber crystals are not mood rings, or whatever. Lightsaber does not automatically change color based on your Force alignment. It is a conscious ritual to deeper one's connection to the Dark Side of the Force. It mirrors the way the Jedi seek for their crystal when they are Younglings, which also only serves the purpose of deepening their connection to the Force.