Actually, it's a bit harder than that... Both of these companies have transaction volumes in a high enough range that they can afford to be their own aggregator and process their own transactions. Any new company would have to work with an ISO/MSP, which places severe restrictions on what kind of transactions they can handle and how, and the fees paid. For example: waiting more than seven days to capture an authorization can double or triple the rate with some banks (SVB's Merchant E-Solutions shows you such warnings in the virtual terminal, for example), and exceeding a certain rate of transactions captured over seven days after the fact can cause a shutdown of your account. (My contract with MES has such a clause, for example.)

In other words: if it were "that easy," there'd already be a lot of competition. But, Visa et. al. aren't real big on letting just anyone be direct inputs to them and the kinds of activities we're talking about here look a lot like fraud to existing ISOs/MSPs.