Sometimes it's because you are encountering someone with a cognitive style that is oriented towards precision of expression. This is an admirable trait that can expose hidden assumptions and lead to valuable insights.

Unfortunately, attacking the form rather than the content of a position can also be an effective tactic for undermining an opposing view without having to risk justifying oneself. It consumes energy without contributing anything constructive. If there's a genuine ambiguity and a desire to work together to learn something, there are usually ways to clarify your opponent's position that help both people reach understanding.