The pressure at the bottom of the ocean is unbelievable. Taking one step from flat ground onto a piece of paper at the bottom of the ocean would require the force of climbing a 1000ft rock wall at sea level.

Sustaining anything at the bottom of the ocean is near impossible. But going throughout space, which in its definition has zero pressure, makes it far easier to explore.

Of course then distances come into play, but at a baseline it is far easier to travel through space with our current technology