He assumed he didn't have CoC(underestimated)
He chose to slowly attack a swordsman in melee rather than blast him with rapid fire lasers, or kanabo air blasts and use kanabo followup in dynamic combat as he did vs pre advCoC Luffy or Yamato here.
Zoro was putting all his energy into asura, he couldn't deal with a rapid fire assault from a far more mobile enemy, it was PIS.