>>12211710I "have" selective mutism and can attest to this.
Another major reason is fear of faliure, I had been ridiculed a lot when I was very young (due to my extreme introvertedness), so it set it very deep into the brain.
This lead to even more social disconnect (was a complete game addict) till I started putting myself out there and learning the shit I should have learned when I was 10.
It all leads down to the abnormal way kids are growing up nowadays.