But that's a hassle.

First you have to figure out how to use the webpage / app to get the virtual credit card number. Once you know, you still have to log into a separate service and click a few buttons. With PayPal or Amazon Payments you just click your password manager's button to log you in right in the checkout process on the same webpage.

What's a virtual credit card?

Some banks will issue one-time use numbers for your cards, limited to a certain transaction amount and then they're gone. A pretty cool idea, but until they have an app that generates these numbers at the push of a button nobody really uses them. Too much of a hassle.