A few things:
1. I think most athletes who purposely ingest a lot of carbs are probably not using sugar to accomplish this.
2. Greasy food is not actually bad for you. Grease is essentially fat, which is about as healthy as you can get. In a typical fast food meal, the greasy burger is the healthy part (minus the bun). It's the fries and soft drink which are the unhealthy part.
3. Grains are an incredibly affordable source of calories (it depends on the grain, but for the most part they are all upwards of 2,000 calories for $1). I don't think anybody's in danger of starving if sugar is more expensive.