AT&T's original plan was to sell DTV (the service that had peaked) and hold onto AT&T TV (the new service they had hoped would grow and which they had put their own name on, positioning it as the intentioned flagship cable TV service). But TPG didn't want that. They were reportedly concerned about DTV customers cancelling and moving over to AT&T TV. In return, I imagine, AT&T said "If you're buying AT&T TV, then you're buying Uverse TV too." But as you say, yes, it would have been complicated to separate the two services out. I think it could have been done, though, although once the current set of universal carriage contracts with networks expired, each service would have to negotiate their own set (as Uverse TV had originally done separate from DTV).