This is very good point. Often our tacit knowledge about how to communicate is much larger than the explicit theory. When people then use a framework to communicate, they sometimes actually get less intelligent in a way because it ignores all the implicit rules.

NVC sometimes seem a bit dry or rational and practioners ignore a lot of tacit knowledge they have, which is why it feels insincere. It also easily promotes a kind of disconnection from your feelings by taking a meta-stance, which can make it actually harder to communicate.

I do love the basic idea and spirit of the framework though, I just think it's not a good idea probably to approach it as a set of rules for how to communicate.