Hashirama is Edo, so it's not doing much damage. Plus, the bigger threat here is eyeless Madara who speed blitzed Naruto and Sai; with the latter being the Speed Blitz King. So things are getting pretty serious.
Same reason Black Zetsu was able to possess and use Obito while Minato( who threw a kunai in the air and teleported to it whilst Ay's hand was inches away from his face) and Tobirama just watched.