USA is just cheaper now because demand has dropped off. The flights may be cheap, but holiday makers know the accommodation, the food, the entertainment, even the shopping is expensive over there. It's an expensive holiday regardless of the airfare so airlines lower the price to pick up whatever demand they can, as it's really only those small number of rellies and business travel that keep the plans to go.
Asia on the other hand still has the cheap accommodation and food, so travel stays maintained as a holiday destination. And on top of that those sectors also get sales for travellers to Europe which keeps a base amount of demand as well. Whereas very few go somewhere else via the US. Travel is virtually only as a destination so is more volatile based on demand for the US itself. It's not a fair comparison you're making.