If first mover advantage in internet payment processing was important, CyberCash would still be around. I'm pretty sure there was another internet payment processor around before PayPal too.

Setup was harder, and the integration wasn't the same, but it was before PCI, so integrating with CyberCash meant you could own the whole payment flow, and have a better experience than PayPal, where you send the user off, and when they come back, PayPal may not have confirmed payment yet.