Why Doesn't a Nationwide IPTV Service Exist?

This isn't some sort of crazed rant, and the question isn't rhetorical. Forgive me if the answer is obvious, or this has been explained a thousand times. I'm really just asking for clarification here. Why are IPTV services only available from internet service providers?

VoIP services such as Vonage, Skype, or Google Voice/Hangouts, are standalone and location-independent. With Vonage's ubiquity, I can't imagine that nobody is trying to build such a service. What is getting in the way?

Is it content providers not playing nice, or is it a technical issue? Or, is it something far more complex that can only be explained in a lengthy comment to this post?