Customers can pay through Visa whether they have a credit card or not:
https://en.wikipedia.org/wiki/Visa_Electron
https://en.wikipedia.org/wiki/Visa_Debit
As far as I can tell it might be only USA banks that don't issue these kinds of cards as standard, in place of a bank card.
I'm not sure about other countries but in the US, it is possible to open a bank account without a debit card attached to it.
For instance, https://www.paypal-cash.com/index.html
People here get useless Maestro debit cards. You can only get Visa/Mastercard credit cards. And very few people do, usually only people who travel to the US bother.
Not having a credit card is the main reason I see for people requesting PayPal (they may also prefer it if they already have an account, but that's not a deal breaker).
People use PayPal from person to person for B/S/T forums. The PayPal user base is bigger in this community because anyone can accept payments without being a merchant, yet unlike dealing over Venmo there are still protections for the buyer.
Also, accepting payments worldwide is much more feasible. Stripe is in 25 countries [1]; PayPal is in 200 [2].
[1]: https://stripe.com/global
[2]: https://www.paypal.com/us/webapps/mpp/country-worldwide