At the risk of explaining the obvious, that's the point. It's how people feign interest in others in order to maintain a socially acceptable level of friendship. The point of the meme isn't the words being used but their frequency. Basically, if you get THIS many dangs and yups in a row without a single actual question, that's a pretty clear hint the other person isn't actually THAT interested in your story but doesn't want to risk offending you by forcefully cutting you off.
Someone who's actually interested will ask you relevant questions. Dangs and yups are just encouragement to help you unburden yourself of your thoughts without them needing to take ownership for them.