Or maybe they don’t. They probably say and do many things of exactly the same nature, and don’t even realize it. They’ve just fixated on this one, because it’s so easy to spot.
Many things that people say–things the just about everyone says, unless they’re autistic–are used to facilitate conversational discourse. They aren’t “filler.” They are just ways to convey stance, affect, etc. without coming across as a total asshole. The people who claim to speak in purely referential and propositional language are just fooling themselves. They, too, use language in this way, when nobody’s looking. Utterances such as thanks, uh huh, okay, etc. are not “filler.” Pragmatically they function in non-propositional ways, but they serve a purpose, such as communicating affect, showing that you’re paying attention, etc.
This isn’t to say that “mansplaining” isn’t real. That’s an entirely different issue.