What I cannot figure out is what that quarterback run would have done for them, even if it was successful.
There were 14 seconds left, and no timeouts, at the 40 yard line. This would allow the Cowboys to take 2, or maybe 3 shots at the end zone.
If the running play were successful along with the spike afterwards, this would allow the Cowboys to take only one shot at the end zone from the 25 yard line.