Why is the mass and size of marine crustaceans greater than the mass of terrestrial crustaceans?

Among marine crustaceans, several species of large crabs are distinguished. For example, the Giant Tasmanian crab or Kamchatka crab are large in size. Among terrestrial crustaceans, one can point to woodlice and similar creatures. They are much smaller than their marine counterparts. There are objective reasons for this difference:
it’s much easier to get around at sea. There, body weight is significantly reduced. Therefore, marine crustaceans do not feel as much pressure. They get the opportunity to move more actively and grow more;
more food in the sea. Terrestrial crustaceans do not have such a plentiful and rich diet that their marine relatives. Therefore, their types have acquired a modest size;
the terrestrial environment is more hazardous. After all, predatory animals and people live on the surface. Therefore, crustaceans have to hide in order not to become prey. They are not able to withstand animals or humans. Accordingly, in order to survive, they must be smaller and more invisible. For example, woodlice prefer secluded, humid places, hidden from the sun and prying eyes. Marine crustaceans have almost no natural enemies. They have no one to hide from and they were able to develop into large creatures.
Thus, differences in size are due to differences in habitat characteristics. Terrestrial creatures are forced to hide, and sea crustaceans have no enemies.