That's good geological info. But you re talking from an economical POV. The OPs question is more akin to what does it take to mine asteroids or Antarctica.
Let s take oil, as you said it is associated with continental shelves while deep water rigs mark the future or that industry.
Same with its...
It's funny you mention that as I am these days sketching a semisubmerged temple of assembly (church, mosque, concert hall)
The OP is asking why not more people live normally at sea.
The ocean is permanently inhabited by humans but those humans do not live permanently at sea.
The research and...
We are, slowly, colonizing the oceans but we re not there yet. In the past worms prevented Maritime nations from keeping permanent floating bases. In the age of steel corrosion (and its upkeep) prevent It.
But from the 70s onward concrete has proven a perfectly suitable material for permanent...