I assume just normal credit card payments online? PayPal started because people were scared to use their card online, but now you get all the same buyer protections and insurance.
Obviously you can do a SEPA transfer as well, but it's not instant and you have to type a long number and don't have a consistently good user experience.
Bank apps lack good UX. Stuff like "send this friend 5 bucks again, this is his profile picture" and are a pain to log into.
I don't say I like paypal or banks, i actually dont like either. But paypal is just more convenient.
For a merchant; PayPal fees are quite high, their merchant support is abysmal and you have to be a decent size SME before you get a dedicated account manager.
And dont even get me started on their so called "merchant protection" offer for disputes.