Just for security reason. When you make a purchase with a credit card you never know if the shop server is well secure.
When you are a small business you do not have the same means to secure your server than Amazon or Ebay and even them has been hacked by the past.
Paypal send an email to inform about the transaction and you can denied it. Most of the time your Bank do not.
With Paypal you can configure your account to not agreed transaction if you have no money on it. You can enable an SMS security if someone try to modify any personal informations. With a bank most of the time it's not the case, if you do not have the money on your account they will accept the transaction to be able to charge you some fees.
If your credit card number has ben hacked, it's going to be very difficult to reclaim your money at your bank in Europe and specially in France, they will always try to denied it. At the end you may be refund but months after. With Paypal it's going to be hard too but much less.
For non electronic items you can ask for a refund if you do not receive it, with a bank you can't.
Anyway my favorite way of payment it's not Paypal but Paysafecard, for me that the best way to pay for non physical item.
And sadly in my countries it's difficult to have prepaid cards (Spain, France)
Best Regards
Nexus