Memes

I get the meme, but I'm going to be pedantic: submarines are full of air at atmospheric pressure so therefore they can be crushed. Living things are full of water which is effectively incompressible so they can't - they'll always have the same pressure on the inside as on the outside without changing size.

This is the reason human scuba divers can go quite deep without feeling any discomfort. Humans do contain big air bubbles: their lungs. The lungs aren't crushed because the scuba equipment automatically provides air at the same pressure as the outside water, but divers have to remember not to hold their breath as they swim up - as the water pressure decreases, having all that high pressure air in the lungs can rupture them. (Lungs withstand being squeezed much better than being stretched so that's why free-divers can hold their breath while swimming down.)

The reason you can't just scuba dive to the bottom of the ocean is actually because the behavior of dissolved gasses in the blood changes as the pressure increases. That's the consequence of pressure that these animals are adapted to.