I am just talking out my ass here, but prior to corporate exploitation I would think the true intention was to create a fundamental foundation for understanding and being able to build upon a personality.
If you understand the categories of your strengths and weaknesses you are better able to understand yourself, cater to what you are good at, and seek improvement where it is needed.
I often fall into the slump of being 'myself' too.
I just get tired (not talking strictly INTP here) of seeing people saying "I am <insert MBTI here> and this is how I am. I am justified and you must deal with it." And so they live their lives according to this and advancement is never made. Now, the advancement is for the benefit of that person, but the more you advance, the better you are able to provide for yourself in life through many means and, in my opinion, through facing struggle and adversity head on you can bring yourself into a higher state that perhaps may be more easily satisfied with life.
Maybe I am wrong, I question this viewpoint every day of my life.