Re: Raumkraut: Because if they control it, they can charge you for it.
If the mobile companies are in charge of providing infrastructure for and managing near-field comm payments, then they'll have another revenue stream: transaction fees.
Whereas, if the credit card companies have control, and the NFC transactions are simply "bits passed upstream to the Internet," then the carriers won't be getting as near a big chunk of that pie...
NFC is bound to be a boondoggle, anyway... Cybercrooks have already figured out how to skim all manner of magstripe and RFID payments systems (no-name ATMs and point-of-sale terminals in corner shops/convenience stores come to mind); it boggles the mind that we'd create yet another avenue for ID theft.
Cash may be clumsy and inconvenient, but it's identity-agnostic, and doesn't rat out your account numbers when it's stolen...