Originally Posted by filip00

Correct.

It's much easier to secure someone from vacuum than from the depths and crazy pressures that are experienced in the bottom of the Mariana trench for example.
It's much easier to track and communicate to people in space, where there are NO OBSTACLES for radio wave communication, whereas in the sea, the opposite is true.
Thirdly, we have mapped the whole moon, because all you need is a telescope. To map the ocean floor, what do you think is necessary? That's a question for you to answer.

With the first two answers that I've given you, and the third one you can answer yourself -> you will answer the whole conundrum that bothers you.
Spoiler alert: