Yeah, they have grocery stores. That doesn't hurt the point here. They can sell it to me there and get $X from the grocery store. They can also take it to the ice cream factory and get $1/2 X.
Do you know why that is? Why would that farmer do that? It's the same thing that's going on here, and neither AT&T nor the farmer loses money by doing it.
What this shows is that both of them have excess goods. The farmer CAN'T sell me any more because there's more than enough milk in the store already. I can't drink any more. Likewise, as many have said here, AT&T has more bandwidth than they need. So what to do with it? Well, clearly, selling it to ANYONE at ANY price is better than letting it go to waste.
So that's what they're trying to do. They give better prices to the bulk buyers just so they can get money for what's left over. It'll go to waste otherwise. People won't buy more milk than they can drink and AT&T apparently can't get people to sign up fast enough to use up all their bandwidth.
"But wait," you say. "Doesn't that mean AT&T is charging more than they should? Shouldn't they be giving us 6 GB for $30 then?" Well, that's a nice theory, but now you're thinking like a good ol' socialist like Hugo Chavez down in Venezuela. They like to do things like set price based on production cost.
It's a legitimate viewpoint! You're free to hold it!
But here in the U.S. both Wall Street and the U.S. government tends to favor the 'invisible hand' theory of Adam Smith. That means we base cost on demand. It's just how things are done here. And that invisible hand is telling us that 3 GB for $30 is appropriate.
So AT&T charges that and then they end up with extra bandwidth. They can either let it sit there doing nothing or they can try to sell it to Netflix. That's their motivation...to earn money off of something that's currently doing nothing for them. That's a big win for them if they can pull it off.
You're arguing that the U.S. should be run more like Venezuela and that AT&T should be taking that extra bandwidth and just dividing it up amongst everyone. That's a defensible viewpoint, but very, very unlikely to ever happen anytime in the near future in this country.