Most prosaically, Chase moves money to the merchant, so that BoA doesn't have to move money to someone who is not their customer and who they have no direct rel

Most prosaically, Chase moves money to the merchant, so that BoA doesn't have to move money to someone who is not their customer and who they have no direct relationship with. They just pay Chase a mindbogglingly large amount of money every day and trust Chase to sort out the logistics. (Back in the day, this would be easy for Chase to do because the merchant banked at Chase, but this is very not guaranteed anymore.) Chase (or a party related to Chase) also had the job of making sure this merchant got signed up to accept Visa cards. They had the boots-on-the-ground salesforce to make it happen. Chase also performed underwriting of the burrito shop to determine whether they are creditworthy, because the purchaser is not the only person being extended credit here -- Chase has a more-than-notional exposure to the merchant's health as a business as well. Why? If you call BoA and say you didn't get your burrito, you will get your money back. BoA is willing to give you your money back, very quickly, because Chase is always good for it. Chase will generally attempt to recoup your money from the burrito shop, but in the case where you are dissatisfied with your burrito because you didn't receive it because the burrito shop went out of business, Chase (and not BoA or Visa, importantly) takes that loss on the chin. (This is less relevant for burritos sold in person, because proprietors very rarely drop dead after swiping cards but before handing over the burrito, but is far more relevant for more complicated business models.)