Maybe your notes were suspected to be plagiarism due to the match with your blog. Or maybe Facebook knows you have the right to carry them but doesn’t want duplicate content for SEO reasons.

In general, Facebook gains by forcing you to give them special reasons to keep your content, because this way it collects information the competition doesn’t have (e.g. a copyright status database) and it bullies into never leaving the walled garden instead of using competitors like your own website.