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Actually lots of places sell unbranded (also known as Unlocked) phones. You can buy from the manufacturer's website or from box stores like Best Buy. These are unsubsidized phones, so expect to pay a lot more than even retail price for a branded phone.

Of course, some of the phones released by companies are exclusively available from a wireless provider and cannot even be purchased directly. But these phones are generally specifically made for the provider. You can't really complain about a product that is only available from, say AT&T, having AT&T firmware.

As long as people expect cheap phones, there will be branded phones available. It actually provides the widest selection. Lots of people can't pay $700 for a phone and those people are only able to have wireless phones BECAUSE of branded phones.

Those who want other options have them available. Everyone wins.

Expecting a provider to literally give you a very expensive phone (you don't think AT&T only pays $49.99 for these products I'm sure) without promoting it's services via the phone is entirely unrealistic.

So the direction "around" it, is to pay full price for an unlocked phone.