Why Yanji seafood is cheap?

Because it is sandwiched between China, North Korea and Russia. Yanji seafood is cheap because Yanji is located at the junction of China, Russia and North Korea, stuck between China, North Korea and Russia, facing North Korea across Tumen River and bordering Russia. Both countries are rich in marine resources, with a wide variety of seafood products, and neighboring countries provide a steady stream of fresh seafood, so Yanji seafood is cheap.