What you're missing is that once you have a PIN the deniability goes out the window, so you're now on the hook for the fraudulent purchases. So as a card user

What you're missing is that once you have a PIN the deniability goes out the window, so you're now on the hook for the fraudulent purchases. So as a card user you're trading a high percentage of fraud with no liability for a low percentage of fraud with absolute liability. Things are better for the bank, not the customer.