Picking a fight with an 800 lb gorilla, startup marketing 15 years ago
I believe WePay provides something that Paypal doesn't (or atleast not easily ) i.e. ability to split payments between multiple users/collectors using multiple accounts. Paypal X/adaptive can possibly provide some of this functionality but WePay does it better and signup is much easier is my guess.
In time WePay may evolve to be revolutionary. Remember once upon a time all paypal was a peer-2-peer money transfer service.