This is because PayPal lets users store credit from when friends transfer money over. It also offers buyer protection so that users can get their money back in the event of a bad deal. However credit card companies are definitely feeling the heat which is why they have since joined forces to create a new checkout button.
Visa and Mastercard already have their own options, but together with American Express and Discover, they plan to join forces towards creating a unified button that will encourage customers to use their credit card services instead of PayPal. The system is still in development and the companies don’t expect to move customers to the new system until later this year.
It is unclear at this point in time what kind of features this new service might have that would offer an advantage over PayPal, so we guess we’ll just have to wait and see.