The three crabs you left in the trap communicated a distress call, warning off their brothers. You should have removed them after they found out the trap was not a two story condo with free food.
Always remove the crabs after checking trap, and rebait with fresh fish.
Find the mud and the crabs will find your trap.
I never heard that crabs will communicate a distress call, all they know is that they are eating. Also bay grasses are the blue crabs habitat. You will have more luck in bay grasses then mud.