Sure. That is their form of access control. They broadcast their streams 24/7 to everyone. (Sometimes even to those who don't need/want the signal.) To prevent theft they scramble all of the content and rent you a box to decode it.
The Internet doesn't work the same way. The Internet has a lot of public content that has no need for encryption (you already mentioned YouTube) and you propose that we encrypt it and make the Internet slower? Why exactly? Just 'because we can'?
With all of the SSL MITM/sniffing stuff aside, the IP connections can still be logged and the data flows measured. What you are doing can still be assumed. You can still be implicated for connecting to a naughty site, etc.
For example, say you connect to an adult site from work and this site is entirely https. Your boss still knows you were looking at porn on company time. He cares not which individual image or video you downloaded.