> why does it matter where they're fishing if they're selling it worldwide?

Regulation. Chinese boats fish in ways we block our own boats from. Those exports thus represent a regulatory workaround, victim the oceans, and a tool with which buyers can demand reciprocal regulation.

How does the worldwide sales address the damage they cause to marine ecosystems? That too when many countries regulate their own fisheries industry to avoid the same issue? This is like strip mining public property or someone else's private property without any authorization. Essentially, China makes money at everybody's expense.

Who makes the profit? Duh.