What linguistic or training factors predispose ChatGPT (and most LLms that feature its API) to often use the structure of “It’s not X, it’s Y”? when generating replies?

More often than not, I feel that the vein of that answer will pop up in the generated reply. No matter what the query or topic. I' usually don't closely follow the updates of each version, but to me it seems an addition that was rolled out in the last 18 months or so.