Because this kind of behaviour is endemic in emotional abusers. There will always be something else that annoys them. Emotional abusers look for weaknesses and exploit them mercilessly. They don't really care about the issue and will move on to something else, ad infinitum.

This is the very reason why you never give a bully or a narcissist a single inch. What they are trying to do is keep you off balance, make you walk on eggshells and create a bubble of control.

If it's genuinely something that is causing a problem that is completely different from the typical needling/whining/unnecessary argument escalation over trivial bullshit that an emotional abuser will mete out.