Ah, understandable. The difference is, fluid pressure is omnidirectional, unlike the pressure from a pair of pliers or an industrial hydraulic press that would crush things "flat" in a particular direction.
A railing of hollow metal tubing sinking to thousand-meter depth could be crushed flat, like a paper straw with the air sucked completely out of it. But if it's not completely airtight, the high-pressure water will force its way inside first, so that the pressure inside pushes just as hard on the interior of the tubing as the pressure outside pushes on the exterior. Similarly, any piece of solid metal just gets squeezed equally from all sides, so it doesn't deform.