Does the "social media bump" definitely exist, especially for Twitter?
Even this article seems to indicate it didn't. Less than 2% of their page views were coming through Twitter. That's practically a rounding error, in spite of them at the time having quite a huge account.
Do people really click links and leave the site in any meaningful numbers? Click through, linger, read articles? Or do they just read the headline preview and then go off on their opinions? Especially for a serious, careful news organization like NPR, I really doubt it.
You're on Twitter to Tweet, not click links and read articles.
Twitter's value, I feel, was always in news discussion -- not article reading -- and #brand nonsense. There's really no good reason for any major news agency to be actively posting their content to it.