Hypothetical Use Case: A bunch of agents and I want to use a XMPP platform hosted by the cartel to raid the cartel and even if they suspect we are agents and even if they backdoor eJabber's own E2EE it would be literally impossible for them to decode the messages as we shared our OTR keys ahead of time on a private LAN or a USB or a stack of QR codes or some punch cards or ribbon tape strapped to carrier pidgins and have our own E2EE on top of their pseudo E2EE.
Dictionary: I created the term pseudo E2EE for any of the big centralized platforms that claim to use E2EE and use some client encryption magical incantations from code maintained by said platform. This is not real E2EE regardless of what magical explanation anyone gives.