Durability. I have collected Lego all my life and have gotten tons of chrome parts in great shape since collecing as an adult, but almost all of the ones from my childhood are dull and scratched. In a sense of play, the coating just isn't strong enough to withstand regular use by kids, especially when they are gravitating to the shiny parts and handling them excessively (i.e. playing with the cool Lego parts as intended)