If internet uses the same infrastructure as cable tv then why isnt tv programming online?

Couldn't TV channels use tcp/IP packets and your TV service could be online or included in your internet plan? Imagine being able to watch TV wherever you get internet access even on a laptop or smart phone by using an account so you can watch in places remotely . Why isn't it like that yet if they use the same infrastructure and wires? Why do you need a TV and coax to watch cable channels still? Slow evolution? Will all TV someday be online? Imagine all telecommunications using the same network except for basic radio. I think it would be easier and less complicated that way. Don't you think? I heard eventually you may be able to connect to the internet by just using power lines and the standard power outlets. Is that true?