Question: In the near future the demand for resources only rises due to both a ever growing population, energy and resource crises, and rampant consumerism. Peak oil has been reached, scarce resources like platinum, silver, and other rare metals have been depleted on the surface, and the world is beginning to feel the more drastic effects of climate change such as mass extinctions of animals and strains of crops. In this rather bleak period the major mining companies looked to the seas to solve the mineral requirements of earth. While mining the seas isn't a easy affair the ocean's mineral wealth is virtually untapped.

However instead of using drones to mine both ores and the methane ice the big companies used mainly human labor (with drone assistance), but why? What benefit would human laborers in deep sea rigs have over a aquatic drone?

Note:

The population is fed mainly by cultured meat and indoor+vertical farming hence why the population is expanding even though the climate looks bleak.

Asteroid mining isn't considered a good alternative for earth due to the transportation of the goods back to earth. However if necessary the industry does exist (mainly for the initial space colonies)

The mines would be accessed by either mining ships or for the larger mines maglev trains connected to large underwater bases (with the tunnels dug under the ocean's surface)

Answer: 
The mining companies are being subsidized
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Drones would have been better value for money, but the government subsidizes human labor.
This is done to keep the population (especially the men) occupied and also safely locked away, not giving them a chance to sit around talking rebellion.

This is also the reason space mining is not favored: there are too many places to run and hide once the tech for space colonization exists.
Gimelist showed quite convincingly why humans are not needed in the Deep. Depending on your reason for wanting them down there, you might be able to introduce them to the Not So Deep.

If the Climate is still in the throes of change, using the surface of the ocean might actually be more expensive than being 30-80m below (ice, storms). So you might have large submerged (pre)processing facilities run by humans, and catered-to by the drones in the Deep. Nice claustrophobic setting, actually within (economic) technical reach.