Trump didn’t shake Pences hand either. It’s not protocol to shake their hands at this point so it would not be expected or anticipated. He was already turning towards the podium when she extended her claw so he most likely didn’t even see it anyway. There are other points to this as well like Pelosi not giving Trump the traditional introduction.
He didn't extend his hand, either. Look, I'm not gonna get in a twist over how Pelosi acted. I expected no more, no less, and she delivered.