Why doesn't the crescent gecko have eyelids?

the crested gecko has a clear membrane called a brine. This brine allows them to have their eyes fixated at all times. Living in a tropical envoirenment, the crested gecko is exposed to rain daily and the rain is able to slide off the brine. This also allows the gecko to have a view of it's surroundings at all times. Because the crested gecko is an semi aboreal species, they do not need to dig into soil often. Most gecko species with eyelids are able to close their eyes while burrowing.