Mining is also quite expensive. Conceptually, the process for lifting from the deep ocean is quite a bit simpler: attach the load to an airtight bag, and release a little bit of air into the bag. The load will float to the surface. There would still be a process involved in getting compressed air to the deep, but it might be simpler than boring holes in the earth.

Of course, it's still likely that the costs involved mean this idea wouldn't work in today's market conditions. That doesn't mean that conditions would never change...

Quite a bit of mining involves picking stuff up off the ground. The worldwide mining industry is surprisingly small due to it’s high efficiency.

Across all materials from coal, diamonds, salt, copper, etc it all adds up to just ~600billion per year in revenue and profit margins that jump all over the pace from year to year.

PS: Rare earth minerals are also generally discarded. It’s the effort to remove them from ore that’s the issue not finding them.