Simply because no one understands, and no one seeks to understand.
It was with blind optimism that I believed that Susan Cain's call for the need to understand introverts would slowly change the landscapes in which introverts can operate at, including society and workplaces. (By the way, her book should not just be taken to be about introverts, but also about the under-utlised talents of introverts. If 1 in 3 people are introverts, then why should we not include them for a 50% increase in productivity?)
Nope, that future did not come to pass. Each time I bring out the phrase "I am an introvert", the conversation goes back to the usual mistaken traits of shyness, social awkwardness and silence. Certainly they should realise that these traits can be mutually exclusive of introversion, and that there are also shy extroverts, socially awkward extroverts, and silent extroverts.
I love talking about topics I'm passionate about, I have a strong preference for deep connections with my social circle, and I do at times enjoy taking a step back to watch and hear the bustle of life around me. I am a proud introvert.
I'll be happy to share what makes an introvert, but first, empty your cup.