That’s because Twitter is struggling to compete with rivals like Snapchat, Instagram, and Tumblr, all of which are designed to keep users in rather than continually sending them out to the broader Web to view content.
Facebook is doing much the same: Its recent big push for native videos and Instant Articles—content hosted within the News Feed, rather than linking out—is ostensibly about a more seamless user experience. And, sure, that’s part of it. Facebook’s own research has told it that users hate clicking on links and waiting for pages to load in their browsers, particularly on their phones, where many websites still look terrible and function poorly. But it’s also a land grab on Facebook’s part, as I and others have explained. The social network is using its enormous active user base to persuade the media to give up control of their content and hand it over to Facebook. If they don’t, they’re likely to find that their links are bypassed by Facebook’s billion daily active users in favor of videos and stories that appear at full length directly in the News Feed.
Exactly this. Pick your poison, got to attract readers/viewers somehow and it's a heck of a lot harder to do so on a self-hosted platform.