Why now?
TV shows need to be online. I'm sure they don't want to be. TV shows can make a lot more money off TV ad revenue than online ad revenue (fewer commercials online). They are going pirated and put online regardless, so it is advantageous for the parent company to distribute them legally with ad revenue.
Why the shift from cable?
Many people are feeling stressed from the economy. They are starting to look at what is expendable in their daily lives. Three monthly expenses immediately come to mind for most people: tv, internet, cell phone. With the age of online video, the standard television is becoming more and more obsolete. It probably won't ever become entirely obsolete, but the internet is pushing it in that direction.
Take a look at what people on Twitter have been saying:
It comes down to this: why buy the cow (Cable) when you get the milk for free (TV shows)?
Read more about movies going online here.