I think part of it is them being self conscious but I think it was also just seen as a "cool" way to behave like you said. I often saw this mentality on reddit of course and in various discord servers where people just couldn't back up what they were saying - so someone else approaching them with an in depth take, just causes them to try and shut things down with "oh its not that deep".
Like its a very dismissive phrase meant to shut down conversation.