Stripe is not a "credit card processor", and that's not the point of OP's comment. The point is that being the intermediary between merchants and processors is the valuable expertise in terms of an OpenRouter acquisition.
It's been a few years, but I used to work on almost exactly this (not at Stripe, but we processed hundreds of billions annually). If you're a big enough merchant (or Stripe itself), you can choose to send a credit card transaction to any one of potentially many processors, each of which have their own performance characteristics (one may approve at a higher rate, the other may charge better fees, etc). All of this subject to attributes of the transaction itself (ticket size, geography, card type, many others). You know quite a bit about the transaction itself before you send it out, so you can build up routing knowledge to optimize for whatever thing you care about (usually transaction success rates or fees).
See how this starts to look a lot like OpenRouter with money instead of tokens? I'm not sure I 100% believe that's how it'll shake out, but there is a transferable skillset.