How is anyone surprised?
If he copped to it, he'd kick up an even bigger fuss than we're seeing right now. The fact that he denies it is, from his POV, advantageous because he can hand-wave away the biggest detriment to his campaign and some folks will just take him at his word here which, again, is a better deal for him than everyone knowing he's a scumbag based on his own admittance.
He was always going to deny this, try to sweep it under the rug and push forward. It doesn't matter if three people decide he's innocent because of this denial, that's three people that wouldn't hold that belief if he admitted to it. In the game of politics, denial of wrongdoing is the most commonly used and essential tool in the toolbox.
The job that we all have right now is to decide for ourselves who we believe. I know that Biden hasn't convinced me of his innocence whatsoever and that's not likely to change. This denial seems tastelessly hostile, obnoxiously arrogant and sounds like gaslighting being aired live on television for the world to see, that's personally not what I ever want in a leader. That said, as these last few years have shown, that actually seems to be just what it takes to get you into the White House.