let me preface that statement a little bit, if you just stand around on the outskirts of a conversation staring at people and not saying a word, not gesturing anything with your hands and not interacting with people is it any surprise people don't know what to make of you?
there are people who go out of their way to try to include people like that but if you run away the moment someone interacts with you then they just assume you're too shy and feel troubled by that so they'll leave you alone out of courtesy to not put too much pressure on you
you can't expect everyone to take on the duty of going out of their way to include you if you make no effort to be included
some people don't hang out with uninteresting people for the same reason you don't, expecting special treatment should not be a given the people who go out of their way do it because they like doing that or want to make people feel more welcome but if you never stand up on your own two feet and make effort to be included as yourself then you'll just learn to rely on them too much and when they aren't around you won't know how to interact with others
tldr; practice being social until you are, if you're heavily introverted hope that a extrovert adopts you as their friend