Yeah, but it would create weird incentives where e.g. if two people are way ahead of the pack, one of them wants to finish after the other. So do they just wait

Yeah, but it would create weird incentives where e.g. if two people are way ahead of the pack, one of them wants to finish after the other. So do they just wait until the rest of the field catches up and then try to trick the other guy into hitting the wall first? Better to just avoid it by keeping incentives aligned with winning your qualifying heat.