Try for too much impact, and you end up browbeating the reader until they're little more than metaphorical pulp. A human writer might like using those types of sentences--or any of the obvious LLM writing tropes--in specific contexts, but they'll usually recognize the need to avoid overusing them.

LLMs don't, and so the tropes get repeated ad nauseam. It doesn't help that social media posts are a huge part of their training data, and there's a large body of research on how Twitter and social media in general have altered grammar and sentence construction towards patterns more commonly found in oral-based traditions as users sought out ways to make their voices heard.

It's easy to imagine a more polished version of a line like "It's not X. It's Y!" being tossed out during a speech precisely because it can be dramatic and punchy. When it's done in every other paragraph, however, it can become rather disconcerting.