Relays composition

The down-sweep pass, or more correctly the push pass was designed to prevent the risks associated with the up-sweep pass, shown in 1968 when the Polish team was winning he women’s 4x100 but, on third to forth, they ran out of room on the stick and dropped it. The Polish coach, later our coach, Gerard Mach, made the switch to the push pass then and there.
As for more opportunities, the up-sweep 's benefit is keeping the arm action in rhythm the whole time, so a miss might require a whole cycle for another try, meaning less chances and not more and looses on free distance. There is absolutely no doubt that the up-sweep requires far more practice time to perfect and is much better suited to teams who know their personnel far in advance and not those relying on trials to sort out the team, like the USA and Jamaica.
The other issue with the up-sweep is training considerations. Since relay training camps are required more often, the possibility of individualized training is diminished and therefor injury risk increased.