Why? He hasn't used Hashirama's Jutsu yet. So what does that mean? This jutsu is powerful enough to stop Madara. Kishi is saving that jutsu for Madara's defeat.
See if the jutsu was used earlier in the game then at best it would have slowed Madara down and not defeated him. You obviously can't defeat a villain during the beginning of his reign.
Example: Naruto learning to throw his Ransenshuriken. He used it almost instantly in the fight with Pain, but he wasn't able to defeat him with it. Had Naruto used that move toward the end of the fight he would killed Pain with it.
The longer Sasuke hold Hashirama's jutsu, the greater the chance of Sasuke stopping Madara himself or with minor help(maybe).
Then Sasuke shall ascend beyond his status of "Lord Sasuke" into "God". Because he would have then beat to demigods.(Juubito and Madara)
See if the jutsu was used earlier in the game then at best it would have slowed Madara down and not defeated him. You obviously can't defeat a villain during the beginning of his reign.
Example: Naruto learning to throw his Ransenshuriken. He used it almost instantly in the fight with Pain, but he wasn't able to defeat him with it. Had Naruto used that move toward the end of the fight he would killed Pain with it.
The longer Sasuke hold Hashirama's jutsu, the greater the chance of Sasuke stopping Madara himself or with minor help(maybe).
Then Sasuke shall ascend beyond his status of "Lord Sasuke" into "God". Because he would have then beat to demigods.(Juubito and Madara)