Part of the definition of "conversation" in the online OED
A nonversation is “a worthless conversation, wherein nothing is explained or otherwise elaborated upon”.
I think the OED editors are right. I think a nonversation is, for the most part, a non-concept. It’s well-known that people who are madly in love tend to say little, and explain less. Are their near-silent conversations worthless?
Who’s to judge the worth of a conversation anyway? Most of the conversations I have on Facebook are of little import, but they’re not worthless because they provide a welcome respite from the general seriousness of work.
Besides, nonversation is an ugly word, a portmanteau word which is as unnecessary as it is unattractive. If you really do think a conversation was worthless, why not call it a worthless conversation?