In Batman v Superman: Dawn of Justice, we see that government agencies and research laboratories are now in control of

• the crashed Kryptonian ship
• General Zod's body

Furthermore, the Indian Ocean is littered with wreckage from one of the Kryptonian World Engines.

Why has Superman left humans to do as they please with these powerful, alien materials?

Even from just an environmental point of view, I find it strange that Superman would not assist with removing at least the largest World Engine pieces from the ocean.