Why is that? Two things: affordability and convenience. It tends to be much cheaper (read: almost always free) to get your content via the publicly vetted general purpose network (i.e. the world wide web), then it is via some proprietary delivery channels (such as your local newsstand, your local cable, etc.) On top of that, it is incomparably more convenient to enjoy the desired content when it suits the consumer, and so this 'on demand' delivery is like a dream come true. Once people experience this kind of freedom, no one in their right mind would ever want to go back to the old, proprietary and costly way of consuming content.
People are therefore abandoning proprietary containers in troves, and are embracing the 'free range' content as it lives on the public web. There is one peculiar detail that seem to have fallen through the cracks, though: no one seems to be aware of the fact that, talking about proprietary containers, a web site is also a proprietary container. Just as a TV cable provider wants to lock customers in and turn them into hostages by disabling them to even begin looking for help, web sites want to lock their visitors/members into their proprietary dungeon, looking for tricks that would prevent them from ever leaving.
However, one thing that the purveyors of proprietary web sites seem to gloss over is that their consumers visit their proprietary sites only because they tend to find the content they're interested in hosted within the bowels of that site. The consumers don't really care about the container that delivers that content.
That sentiment explains why have RSS feeds become so popular. It's the content, stupid! No one cares about your site, no matter how much effort you've invested in prettying it up, choosing the right fonts and font sizes, the right layout, the right colors etc. Who cares? The only thing that matters is the content found on your site!
But guess what: that content is in no way locked in on your site. Other sites can graze the content of your site, slurping it up, repurposing it, making it even more attractive for the consumers than you've ever dreamed possible.
So you, as the web site creator and host, are now faced with two choices: resist and die a horrible death of attrition, as your consumers abandon you, or open up, and die a nice, pleasant death of being swept away by the tsunami.
The choice is yours. But remember -- no one in their right mind wants to visit your site!