I believe the answer to your question is that WordPress.com is a blogging platform that supports original content blogging and Facebook is a social network. I believe
WordPress.com has chosen not to provide to the ability to auto-post content into pages and posts as that is what leads to duplicate content blogs. Note that content thieves use auto-filled content to create splogs and spam blogs. Please see the section in Types of Blogs allowed and not allowed so you know where WordPress.com stands on the issue of auto-filled content.
Automated blogs: Blogs that are generated by computers, including randomly generated blogs, blogs that re-publish press releases, marketing material, search engine results, link dumps or any other mass-produced content.
Google re:duplicate content
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