According to studies from Acacia Labs and the regional Pokemon Research Guild, Arakloon is the typical mature form of the Arakling species, and will often only evolve further with outside intervention. As such, they are able to reproduce and live fulfilling lives in their colonies without ever evolving.
An Arakloon evolving into either a Wighter or a Latrower seems to disrupt the usual social hierarchy, with Wighter being cast out from the colony (either by force or by choice) and a Latrower (typically only one will survive in a colony at a time, as if two ever meet in the wild they always fight) will make her way to the top of the pecking order, killing and eating both suitors and young Arakling she deems unsuitable.