I would not be surprised, if it has been Boeing having pulled the plug. They may not have the money to continue with the 777X (ie setup production facility, for only a few airplanes over many years), especially when their biggest 777X customers (EK, LH, CX) obviously no longer have a need for this uber triple.
Consider the 737Max money sink needing huge amounts of money to avoid a shredding of the nearly 1000 already build jets. Larger hardware modifications might be unavoidable, now the software still does not seem to surface for approval.