Is it that much different than Redditors rehosting images on Reddit/Imgur? I find the functional design of the site terrible but there's tons of popular sites that are based on hijacked content.
Imgur is (IMO) turning into the same thing. Banning direct links, forcefully redirecting direct linked images to their ad packed pages of mostly stolen content.
At least in the case of Reddit it's quite different.
The primary value by a huge margin on Reddit is the text content, the comment / discussion section in each thread.
Pinterest is basically entirely built around the rehosted images they pull in. It's by far and away the primary value on the platform. A distant second is the typically small amount of associated text with a given post.