Lobbying? There are probably a lot of entrenched interests that don't want the ISP/TV provider monopoly to go away. I guess for TV, there are actually 3 to 4 options available for most people (Dish Network/DirectTV/Cable/Fiber). But for broadband, there is usually only 1 option, or 2 if you're lucky, and they also happen to be selling you content.
So why isn't it prohibited on the antitrust grounds? Or they can't be sustainable as separate companies?