There are two things at play here: First, it is far easier to reply to an existing conversation than it is to start a conversation. Expanding on or contradicti

There are two things at play here: First, it is far easier to reply to an existing conversation than it is to start a conversation. Expanding on or contradicting an existing idea is easier than having an original idea. The second is that you are more likely to notice a conversation that has multiple replies so it appears most topics take that form. This is a form of survivorship bias, in that you rarely see the topics that don't start the threads. While I'm sure there are some responses of this nature that are true linkbait, I think the vast majority are not. Most of them are just people wanting to give their opinion, especially if they think somebody else is wrong.