I could go into the entire economics of it but to put it simply: having worked in food exportation you find out very quickly that it doesn't serve you well to export food to the US that has any blemishes and isn't the highest quality. Other countries are far far less picky about their produce. Grocery stores won't except anything but the highest quality produce because if someone doesn't know what they are buying they will google it and if it doesn't look and taste exactly like described they will return it or never even buy it. So now you have spent thousands of dollars shipping something there that no one wants to buy. Businesses aren't out to waste thousands of dollars for shits and giggles. Amercians are spoiled and have far too many options for poor quality ingredients to be shipped there. They quite simply just won't be bought.

There are kobe cows in the US. There are also dozens of other US based cows that many would argue are superior to kobe and han-u. Kobe is good for sashime but not optimal for cooking due to its extremely high fat content. Han-u is basically American Wagyu beef so its importation would be silly for the cost.

Show me this market that grows the highest quality food you have ever eaten in the middle of a major city where they literally pick it for you every morning. I'll snap a couple of pictures of them at the wet market if I come to Seoul. The local markets where i live claim the ecaxt same thing as you. Th "avocado lady" locally tells all the foreigners that she gets all her produce from family in southern china. I see her at the wet market every morning. So please take pictures and show me I would make a specific trip to Seoul just to experience it because food is literally my life. I was trained as a chef, worked in kitchens for 10 years and now travel to find authentic source ingredients for clients in the US.