Online Payments: Why isn’t Airbnb licensed as a money transmitter?

In addition to the answer by Scott Feinberg one must also consider that AirBnB could be an agent of a Licensed Money Transmitter. In this case, they (AirBnB) could be a Agent of a Licensee with the explicit agreement that Braintree would handle the funds processing for them. The accounts to which the money flow (after being processed from Braintree) would be such that they would touch the account of the Licensee. This is all assuming AirBnB is not an Agent of PayPal (as Braintree is not an MTL holder - to the best of my knowledge).

So even though Braintree or any other PSP is processing payments on behalf of AirBnB, the License coverage may be from a totally separate company all together for AirBnB as an Agent. The only requirement is that the Licensee would need to see the flow of funds through them.