"Why is xrp such high value when banks can get so much benefit from Ripple's protocol but without using xrp?"
Let me try an analogy. If Ripple was Google, the protocol would be the Internet and XRP would be the search engine. Your question would be asking why the search engine would be of high value when users can get benefit from using the Internet without using the search engine.
I MEAN, SERIOUSLY, THAT'S THE WHOLE POINT!
Would Twitter be a better business if instead of connecting to users over the Internet (which works perfectly fine without Twitter) they instead built a proprietary network that only connected to Twitter?
You are thinking very, very small. Ripple is thinking very, very big. We're building open protocols and a payment network that can handle the world's payments and that we hope others can get behind. If that's a bad strategy, then the Internet is worse than proprietary networks.
If you had the idea for Google or Twitter and there was no Internet, you'd have to build it. And yes, you'd be building a network that works perfectly fine without the services that will make you money. But that's actually the best strategy -- to grow exponentially the market you plan to serve and sell into.
(I am an employee of Ripple, speaking only for myself.)
RE: Why is xrp such high value when banks can get so much benefit from Ripple's protocol but without using xrp?