Mrs Isabel Briggs Myers invented MBTI to avoid her depression, and played the role of Pollyanna all her life.
So MBTI is for those who want to play the role of Pollyanna and avoid their own depression.
Of course the role of Pollyanna is a psychological defence against depression and sometimes depression breaks through.
Mrs Isabel Briggs Myers was lucky because she lived in a society that loves Pollyannas, just as they love salesmen, and indeed they are selling themselves to one another all the time, so the role of Pollyanna is handsomely rewarded.
It takes someone like myself outside of this culture to see how phoney the Pollyanna role is.