The hitchhiker needed a ride. They had prepared to not be picked up, but they hadn't been prepared for that to last for over a week. They were out of food and nearly out of water. They couldn't afford any more delays; the next driver that picked them up was either on their way to Texas, or they would be by the time the hitchhiker was done with them.
Changing a person just to catch a ride seemed a little drastic, but desperate times called for desperate measures. They weren't all-powerful. The most they'd ever been able to do so far was to change a person's past so that it made sense to drive the direction the hitchhiker needed to go. Back when that trucker had picked them up, he didn't change at all; all that changed was the contents and destination of his delivery. The hitchhiker hoped a trucker would pick them up, but if not... well, they hoped it was a trucker.