Introverted people, in general, are less likely to meet large numbers of people. You rarely have the energy to do "that kind of stuff" (party, high-energy activities, et.al.). Usually, this means that introverts will talk and interact with fewer people, and thus fewer potential dates, in a given period of time. Add in the inability to get comfortable quickly, and the imbalance grows.
That vibe, that energy you emit as a person. It can make people wanna hang around you, people wanna talk to you, girls or boys are more inclined to date you. If you lack that certain energy or vibe than it can be the total opposite. It’s more that just being nice, mannered, having worldly possessions or a silver tongue. Being an introvert myself I know the feeling of loneliness can have. People sense it and they don't want to be around you let alone a girl or guy you wanna date.
We live in a culture that worships extroverts and outgoing people. Extroverts are regarded as positive energy. Extroverts get along best with other extroverts and rarely want to be with introverts. There are no disadvantages of being an extrovert because you have lots of friends and people are drawn to your positive energy. Introverts are often regarded as negative energy/aura by extroverts.