There is still the remote possibility of a fumble or tackling the ball away from the defence in those cases. In the underarm bowling incident it was made physically impossible to win. In baseball terms, he had to hit a home run with the ball on the ground.
(Though as a non-American, I am indeed mystified why the kneel is legal and not regarded as delay of game!)
(Though as a non-American, I am indeed mystified why the kneel is legal and not regarded as delay of game!)