Eventhough j2 2018 was first in the list of 4 devices to be updated in nov. C7 pro was the first to get it. This may indicate j7 16 is very next after that. As j2 2018 is the new phone in the market which is been served as a lower mid range phone got a high market. So they dont want to compromise on the quality by leaving any bugs which may compromise their current j2 2018 sales.
Edit: May be they now want to give only oreo update for a 2018 phone so they are delaying from the beginning.