It probably has a lot to do with the environment of these forums. I've observed casually that many people who haven't been exposed to MBTI forums inclusiveOR have read deeper into typology tend to be more S. I could speculate and say that it could partially be due to Ss being less inclined to join forums about a very "theoretical" concept, or Ss (and Es to some extent) supposed tendencies to not look too deeply into things, which could explain the unusual frequency of introverted Ns on these forums, but I'm not too comfortable with accepting that as a fact. But look at the S stereotypes and descriptions, which someone who is more familiar with it is more likely to encounter. Is it more flattering to yourself to think of yourself as impulsive, short-sighted, rigid, shallow, and perhaps most insultingly, unintelligent... or deep, creative, intuitive, and curious? In an environment that's rife with N worship, why would you want to apply a lable to yourself that you or others perceive as inferior? It's hard to ignore such a pressure. I've even come to stronglyquestion my type as a result of it, and to even question whether some form of intuition is in my top 2 functions. Though I'm sure some are a lot less easily swayed. As for why someone would prefer to be an INFJ over an INFP or ISFJ? Well, INFP stereotypes aren't the most forgiving at times, and the INFJ charicature is flattering, especially compared to the ISFJ one. I think it's more than INFPs or ISFJs wanting to be "more unique".