Which, in my opinion, means that the blame should really go the app developers of these apps.

Who are those people that think it is a good idea to send your medical details (the article also mentions "Flo Period & Ovulation Tracker", which apparently sends whether you may be ovulating to Facebook) to a third-party, let alone Facebook?

(Actually, at least for Android apps there is a answer to who these people are... and there are quite a lot of them: https://reports.exodus-privacy.eu.org/en/trackers/66/)