I don’t know if I’d call it lack of interest but more a lack of need for the amount of work that would be needed to be done.
Discourse oneboxes quite well so it’s simply a matter of copying the URL and pasting it into the post.
And posting content from a WordPress blog into a Discourse topic can be done using the plugin.
As for some type of “share with Discourse” browser or app widget I’m guessing it could be done somehow, but there would need to be specifications first. By specifications, I don’t mean only the “goal” but detailed logic steps the code would take from beginning to end. The if this, then this, when this then this stuff.