USDA[0] says that the US produces 1 million metric tons of oats per year, or 4% of global production. Sure, that is not the best, but clearly still in the game.

[0] https://www.fas.usda.gov/data/production/0452000

In many ways, it's a story about far more than just oats.

US Ag policy is so, so screwed up. But with more entrenched interests than the US has Congressmen, and probably 10X that number of full-time lobbyists - good luck trying to fix it.