>>13780066They do make big holes underwater too, it's just that oldest sea floor is barely 250 million years old with most of it being under 100 million years old.
Example of this would be Burckle crater in the indian ocean, it's under 3800 meters of water which is typical for the ocean floor, obviously small rocks won't leave craters at such depth but big ones will. Meteors or comets come down at speeds of 20-50km per second, water is basically the same stuff as rock at those speeds (or more like rock behaves like water) and land hits can easily effect material 5km down (Chicxulub crater is 20km deep for instance).
Of course another reason why there aren't many craters in the sea floor besides the age is the fact that they are harder to spot, sea floor is more active and features get distorted or buried faster than on land, there's also nonzero difference in the habitability of land and sea and thus way less people are on the sea floor to spot these things than there are on land (this is why north america and scnadinavia have lot of these, not because god hates them (I wish) but because it's a wikipedia list of accessible craters which correlates more with people studying craters than actual craters).
>>13780026Continents are self stable, they break appart and merge but any individual piece is more or less as it is. That's Vredefort crater from 2 billion years ago is visible, because that bit of south africa hasn't collided with anything for that long. Of course you can find craters in the edge areas too but they are harder to spot there.
