If you take a giant whale out of the water and put it on land for long enough, it will crush itself under its own weight. Why doesn't the animal get crushed under its own weight when it's in water?
When it's in water the buoyant pressures are distributed more evenly over the whale's natural surface contour, resulting in less internal strain in the whale's body.
On land, the pressures are all concentrated in a planar surface at the bottom. The whale's body is not naturally planar, so significant strain develops as the body attempts to conform to the planar surface in order to distribute the forces resisting gravity.
One place this issue is discussed is here. The key paragraph is
which is pretty cool. But then this leads to another problem addressed here:
At the same time, as the article points out, the lack of gas exchange is useful in the sense that it circumvents the problem of nitrogen getting absorbed into the blood that would then bubble out at lower depths.