The problem is when you sell X bits for $Y, you'll want to keep X as low as possible and Y as high. Now if bits were fully metered they'd have no problem selling you all they have.
No, AT&T is in the business of selling phone contracts. The actual bits themselves are loss leaders to help sell those subscriptions.
OK, you're right. Maybe it was wishful thinking: they should be in the business of selling bits.
No, AT&T is in the business of selling _access_. The less each customer costs them, the better.