I think you could start out as naturally introverted but being pushed, harangued and harassed to comply in the extroverted world could lead to lifelong anxiety. When you don’t play the part well enough as an extrovert you’re treated as faulty and require more fixing with extra socialising or even pharmaceutical drugs. When you fail in your unnatural environment you get ridiculed or humiliated and anxiety is born.

When you reach the ability to fake extroversion you get left alone. I feel this is area ambiverts fall into.

As for personality disorders. Most people have the traits described in PD but people with personality disorders rarely acknowledge having the traits in the first place.

This is probably incoherent. So, I should stop.