There is no official reason why, but post in France seems to be held up somewhere at present!
I've not had the usual amount of business post this week, and our postman confirms that they are not receiving the usual amount of letters or parcels through the sorting office either, but that there is no indication of any official industrial action. I have business parcels that were sent two weeks ago with an expected two day delivery time, and they haven't yet reached their destination - the post office's tracking system only indicates that they're held up at a major sorting centre.
If you have sent a package to France recently and haven't had acknowledgement of delivery, please don't nag the recipient, it's possible the package is still in the delivery network. Likewise, if you're expecting a book from France, please be patient.