A 17-year-old from Nebraska and her mother are facing criminal charges including performing an illegal abortion and concealing a dead body after police obtained the pair’s private chat history from Facebook, court documents published by Motherboard show.
Presumably they maintain full access because they control both ends. The encrypted part would stop others intercepting messages. At least that's how I've always read it
Edit: I'm wrong, end to end does exclude even the app provider from seeing messages. So yeah, either not enabled or they lied