Because that is where they live, that way they can burrie themselves in the sand to get protection from predators.
The most common predators of sand dolars are ocean pouts and sunflower starfish. Sand dollars do not have many predators.
Sand dollars have these cilia or hair-like structures underneath them that are used like legs. They are used for locomotion and if they are not moving (especially for a long period of time), they are probably dead by then.
Sand dollars have a survival mechanism where they burrow into the sand to avoid predators and turbulent wave action. They can also regulate the amount of water inside their bodies to control buoyancy and help them stay afloat above the sandy bottom. Additionally, their hard exoskeleton provides protection from predators and helps with camouflaging against the sand.
In the sand
Bananas
You can not cheat to get sand dollars. You have to work for it, or you have to buy it.
The sand rat (Psammomys obesus) like most animals that live in a desert environment do have predators such as raptors.
Sand dollars.
Sand dollars breathe through a process known as diffusion, using their tube feet.
sand dollars got there name because they are shaped like a coin and they dig themselves into the sand
Phylum Echinodermata