There's not much to find for 99.99% of both of those. Like, exploring a distant planet versus exploring actual vacuum "space", is similar to exploring an undersea thermal vent versus exploring millions of square miles of featureless silt around it.

Do you really think in caves is more to be found, than on the seabed?

Most caves you will find, will look exactly like the cave before. Different types of rock. If you are lucky, crystals. In the deep sea, you have chances of finding entirely new species. (Only some caves have life at all)

Caves can have intricate ecosystems. There was an article on here some time ago how a single bag of chips completely altered the balance of a cave's fauna and flora.

Both require vast amounts of money. Exploring caves is a lot more affordable (but still not cheap).

melting glaciers are revealing territory previously inaccessible let alone unexplored