I have insisted nothing of the sort. Of course, opinions on words and languages can change over time. However, I find it unlikely that a population of tens of millions suddenly became offended, even if their prophet told them to.

More reasonably, I think they are not offended. Rather they are simply trying to use the full name of the church rather than any sort of shortenings. Sure, if somebody was being a jerk and using the word Mormon to be a jerk, then that could be offensive. However, that's a much different thing than being offended by the word itself used in a friendly context.