Before he begins trying to make the catch, he's not defenseless. But that's illegal contact or pass interference, when applicable. After he makes the catch and establishes possession (such as when he begins running with the ball), he's no longer defenseless.
Taylor lowered his head, too. His shoulder hit Robinson (legal). And his helmet hit Robinson in the chest (illegal) and lower helmet (illegal).
The ball had already bounced away from him. But like I said, that doesn't matter on this play. It wasn't a late hit.
How is that NOT defenseless? He can't defend himself when he's trying to make a catch. That's why he's considered defenseless. He wasn't out there to block Taylor, you know.