Why is a large excoskeleton less limited for arthropods that live in water?

three paits of jointed legs.

Edit: Be Real Man. The real answer is that the water pushes heavy stuff up to make them lighter in water then in land.

edit: really you both are rong the real answer is:Afaik this depends on the animal in question. Some insects, for example, do not grow in size at all when adults and thus avoid this problem. Animals that do shed their exoskeleton can move, the underlying soft exoskeletong along with the internal pressure of the animal are enough to facilitate this. But at least many crayfish (and likewise many otehr arthropods that shed their exoskeleton) hide until their exoskeleton has hardened again - that is, they can move, but will not unless they really have to. They just hide in some nook and wait.

And what comes to other disadvantages of chitious exoskeleton: it allows muscles to attach only inside of the exoskeleton, quite unlike human muscles for example work. This provides poorer strength production, which is why arthropods cannot really grow much larger than what we see around us. For similar reasons, virtually all the largest arthropods live in water, because there you need less strength to move heavy weights.

Even though we know that ants are mighty strong compared to their size, human-sized ants would collapse even udner their own weight and they could not carry a hundred or so times their weight like small ants do!