Why didn't Madara absorb this technique?
This has been explained before, during the battle of Gai with Kisame.

Kisame's technique absorbs chakra from the Ninjutsu technique and grows stronger while the opposite attack grows weaker, but it couldn't do anything about the Sonic Punch, Hirodora (Afternoon Tiger). This is because unlike nature manipulation techniques Gai's Gate technique utilizes pure Taijutsu.

Rinnegan can absorb any and all Ninjutsu techniques, because Ninjutsu uses Chakra to achieve nature manipulation, whereas Gai's technique utilizes the speed achieved by the Gates to create the destructive power of his attack from the atmospheric air itself, and which can't be absorbed.

Also, it is stated in the Manga that Madara in ten-tails Jinchuriki form only Senjutsu and Taijutsu work since he can absorb all Ninjutsu.