Because you can shuffle people into little categories. Humans like to categorize things. Never mind that personality psychologists deride it. In fact, the newest model, HEXACO, goes off the Big 5 model, which is a spectrum model instead of a binary model. Even HEXACO is beginning to fall out of favor. The six dimensions are Honesty/Humility (a measure of how prone you are to be deceptive, sociopathic, and unrealistically self-aggrandizing or self-injuring), Emotionality (a measure of anxiety, neuroticism, sentimentality, emotionality, moodiness, and what might be best visualized as 'how much you are like a little chihuahua who is shaking, running around, and pissing itself'), eXtraversion (this is pretty straightforward), Agreeableness (how much of both a 'team player' and a vaguely over-dependent ninny you may be - if you're super-agreeable, you are probably a doormat, and if you're not very agreeable, you are probably an asshole), Conscientiousness (do you rack disciprine?), and Openness (are you liberal, well-read, educated, worldly, appreciate the intellectual and the aesthetic? You score high on openness. Are you a conservative hide-bound ignorant redneck? You score low on openness.) Never mind, of course, that the real answer is that even if you could separate humans into broad personality traits, those aren't even necessarily completely inherent to the person - I mean, sure, there are tendencies, but culture and our own reasoning and deliberate action has more of an effect on it than we think.
I think this is the first time ever I agree with you on something. I hate the Myers-Briggs and I do believe it's comparable to horoscopes: we see what we want and we use it as a way to mostly flatter ourselves. Another problem I feel is rampant with all these "tests" is that they only measure a person's perception of oneself which may not be accurate at all. I've mentioned here my roommate who thinks she is introspective yet seems more to me to be extroverted, but cripplingly insecure and shy. The first trait drives people away (especially as she covers it with a thick veneer of naive arrogance) and the second makes it hard for her to meet people to replace those she drives away. For instance this New Year's she told me she had decided "we needed to go out once a week [together]" to help her meet people. That doesn't seem like the kind of resolution an introvert would make, at least not if they are comfortable with their introversion. The other thing I don't like about tests like this is they tend to make people perceive their tendencies as unchangeable facts, which then reinforces those tendencies. For instance, you take a test, it says you're an introvert, you then accept the "truth" that you are an introvert (instead of, again for example, shy) and instead of trying to change or grow past that shyness or other quiet tendency (assuming it's something you want to change) you then say "Well it's okay I'm like this. I'm An Introvert." It encourages people not to try to change things. Supposedly, this is me (although I don't know if I'd fall in the I so much...I don't know...) I find this description overly flattering, as in, I can tell that I want to believe these things are true of me and therefore I do not trust that they are. INTJs apply (often ruthlessly) the criterion "Does it work?" to everything from their own research efforts to the prevailing social norms. This in turn produces an unusual independence of mind, freeing the INTJ from the constraints of authority, convention, or sentiment for its own sake ... INTJs are known as the "Systems Builders" of the types, perhaps in part because they possess the unusual trait of combining imagination and reliability. Whatever system an INTJ happens to be working on is for them the equivalent of a moral cause to an INFJ; both perfectionism and disregard for authority come into play. Personal relationships, particularly romantic ones, can be the INTJ's Achilles heel ... This happens in part because many INTJs do not readily grasp the social rituals ... Perhaps the most fundamental problem, however, is that INTJs really want people to make sense.
Also agree! For the longest time I mistook being socially crippled/anxious with being introverted. While I am indeed a quiet person by nature, being a quiet person doesn't mean you should have a hard time conversing with people, a hard time looking them in the eye, a hard time even approaching someone for a conversation. It should only change how you approach meeting and interacting with people. I'm worried that many people like to think their "introvertedness" is fine and good and a perfect excuse to sit in your house all day and not interact with anyone. As soon as I recognized this, I've been able to restructure how I approach and make new friends/acquaintances. Small social gatherings, clubs that promote meeting others through passionate interests that everyone has, etc. etc. Your third paragraph is spot on, ref.
I think being able to tell the difference between social anxiety or ineptness and introversion is pretty important. I've never had a hard time doing any of these things you describe as being central to social skill; I just get worn out more easily from it than others.
If you are wondering about the ability of Myers-Briggs to meaningfully categorize people, the question is not whether your type description is accurate or flattering, but if it is a better match for you than the descriptions for the other types. You may like your horoscope for the day, but you will probably find horoscopes for the other signs just as appealing. Compare the INTJ profile with that for ENFP. Do you have a "great deal of zany charm"? Do you neglect your "nearest and dearest" while trying to "change the world"? Are you "affectionate, demonstrative, and spontaneous" so that you "light up" your partner's life? Does your partner have to handle the practical and financial aspects of the relationship due to your short attention span and emotional needs? Your other objections are not really criticisms of Myers-Briggs. The test need not be a self-assessment. And any personality test could reinforce self-perceptions.
That's pretty close to the conclusion I've arrived at. One career center guy at my college had me take one of those and it came up ENTP/INTP. A career center lady at my original university had me take one too and it came up ESTP/ISTP. Neither of them knew me from anything more than our few brief meetings and each one decided that I was one or the other. Furthermore, neither considered that I might only be that designation when interacting with them. Consider this: friendships are shaped by the perceptions of both parties about the other and the friendship as a whole. That perception informs interactions. The way in which we are friends with a particular person is not the same way in which we are friends with another person. While we might generally act and react in certain ways, context is everything.The other thing I don't like about tests like this is they tend to make people perceive their tendencies as unchangeable facts, which then reinforces those tendencies.
My mother, ever the MBTI blowhard even after I've shown her actual scholarly papers describing why it fails as a test (which is bizarre, because she has a master's degree, which she had to get by defending a thesis, which requires some appreciation for empiricism), classifies me as an INTJ also. I always tell her 'I am not an INTJ and you are not an ENFP. I am a teamramonycajal and you are a momramonycajal.'