The U.S. tied the old World Record, not the American Record. They beat that in the semis and again in the finals.
They select the best starter for position one and want to make sure to have a good curve runner for 3 so that leaves 2 or 4. My suspicion is that he may not be viewed as a good enough passer and his top end speed is close to Gatlin so there we go.
These guys did great by the way, they came to the last leg even with Jamaica. There is the problem with Mr. Bolt, who at present is unmatched, so, nothing they could do about that.