So we all know that Sasuke does not have an arm. And after his fight, Sakura was saying something about making an arm out of Hashirama's cells. Thing is—Sasuke has the Rinnegan, and knows how to use it. So, he can use the Asura Path technique to get a new arm. So what was the need for an arm made of Hashirama's cells anyway? Why did they make one for Sasuke if he can get a new arm himself? And why is Sasuke missing an arm in the first place? He should have had his own new arm by now.
I think it's because sasuke lost a lot of his powers after he sealed kaguya. (Naruto even list his SOSP (sage of six paths) more). Sasuke only had his rinnegan, ad so, I don't think he can restore his arm using asura path technique
When Naruto and Sasuke battle after they defeat Kaguya, they end up both losing an arm. Tsunade implants a certain cell inside Naruto's missing arm's side to let it grow back. But Sasuke does not want his arm to be recovered because he wants to punish (-ish) himself for all the harm he had caused.
Since, as EIPsyKongroo said, he only received the Magatama Rinnegan when he got the Sage of Six Path chakra, and I don't think it has the ability to recover any lost/damaged cells.
Sasuke is of Uchiha blood line , if he implants hashirama's cells in his arm, he will activate a rennaigan in the right eye. He doesn't trust himself yet. So he doesn't attach a new arm like Naruto.
As Troll dé Mage said
- Maybe he wants to punish himself for all the harm he had caused OR
- He thinks that having Hashirama chakra in him would make him too OP and he is afraid that he may turn on the wrong side.
Sasuke thinks he's cooler with one arm or this is his way of atonement or his trying to be more emo or maybe he thinks he doesnt need it yet