CCR "Biology"

So currently in Biology class we are learning about animal behavior and how they survive and have reproductive success. An example of how animals behave that disturbed me was about fiddler crabs. A male fiddler crab has a large claw to use as a weapon and to attract female fiddler crabs for mating and another small claw for eating. When a female crab spots the male crab's large claw she mates with him and she is later kept under mud until her eggs begin to develop. The part that disturbs me is the female crab has to stay under mud until she is ready to give birth. I just believe that out of all places why does she have to stay under mud opposed to a cave or under a rock? However, I can see the similarities between the fiddler crabs and humans. Female humans would normally stay in the house most of the time until they're ready to give birth which is similar to what how the female fiddler has to stay in one place until she gives birth.