Because, if you read the damn words, he promised the Capn that he would!! He was making a powerful point which you, Little Hawk, of all people, should have appreciated. He said to the Capn, "a man ain't nothing but a man..." the implicit affirmation of which is a gamble that to honor his word, he could drive the merely material body beyond its physical limits rather than be beaten by the steam engine; the final proof, in plain action, that the immortal spirit is more powerful than any contraption of flesh OR steam.
Geez, LH, don't you unnerstan ANYTHING??? I'm gonna send you back to TM 101 for a review of basics!!