It being "bad" is subjective. It's f**king annoying as hell, to some people. To a LOT of people, actually. Personally, I don't give a damn as long as it doesn't affect me - but speaking from the perspective of people that do find it "bad",, I'd say it's because like. Ok.
For example, you have a classmate. They are an okay classmate, except for the fact that every time the teacher calls on them, or you hear them talk, everything they say leads back to one subject or they only talk about that one subject. In this scenario, let's just say it's their partner, or their relationship.
This bitch never shuts the f**k up about her boyfriend, and she needs to tell everyone about him and the date they went on last night. You don't wanna hear about that, I don't wanna hear about, we're f**king annoyed. It's the same shit.