Corn??? I don't think corn in bulk is cheaply available in Japan at all. There's a mention in Wikipedia of a Chinese-Mongolian corn meal porridge thing but it looks pretty local.

If you go into a Chinese supermarket, it will quickly become apparent that the default cooking oil is corn oil.

I find this an interesting contrast with the United States, where the default cooking oil is Canola oil (if you're a person looking to cook your own food; this is the sense in which the Chinese default is corn oil) or soybean oil (if you're a company looking to sell packaged food in grocery stores). As far as I'm aware, traditional China would have had sesame oil and maybe soybean oil, and certainly not corn oil. The advantage of corn oil must be the price.

But if corn oil is so cheap, why does the cheapest oil available in the US seem to be soybean oil?