Why can't some people accept that not everyone is interested in them?

I was quite an introvert all my life until 15-20 yrs ago, I dont know what brought the change. As an introvert-people think something is wrong with the individual, they expect you to be chatting & socializing. Since their expectations are not met, one gets called weird OR anti social which i didn't appreciate. You are what you are dear, in this world we must also learn to interact with others, then they see us positively. Otherwise people can be mean.