Why is introversion a disorder but not extroversion?

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Society is messed up. There are so many things wrong with people's opinions, but it's spread through traditions and social media. Maybe because many introverts are bullied because of their quietness, and therefore seen as lesser citizens? Or because quiet people can be pushed around easier so people take advantage of that? I'm not saying all introverts are 'pushovers', many take no shit from anyone, but people have assumed a stereotype and it stuck. There's a quite from Marina and the Diamonds that expresses your thoughts exactly (sorry if its annoying to post, but it's a good quote):
“Why is being a loner characterised as a ‘social disorder’? It makes me never want to speak to anyone again. It makes me annoyed to be labelled as ‘antisocial’/ socially anxious. I am in fact very comfortable in social situations, I just have a truthful and realistic view of the meaning of friendship and relationship-That you cannot get on ‘really well’ with everyone, you cannot even really ‘like’ everyone (though most people pretend to). In reality, each individual probably finds they don’t have a real ‘connection’/ chemistry with no more than 5 real people at any one time in their lives.
I feel like if you don’t get on really well with someone, there is little point in spending time socialising with them. Most events are full of people talking about nothing and this makes me feel even worse than staying at home, alone. Or perhaps I am just jealous of the people talking about nothing and cant step out of this godforesaken bubble that makes me want to never go out again.
Some people need time alone to process thoughts/ events and some people don’t. I will probably always be this way. Every boyfriend I have ever had has been a loner. I wish people wouldn’t make introversion into a personality flaw.”