Those aren't necessarily connected in the way that many people like to assert with such conviction. Many introverts (like me!) love parties and hanging out with friends.
Psychological terms like these get confused in common-speak all the time. I am always a little thrown off when someone describes an asocial person as "antisocial", without realizing that the latter means something very different and disturbing .
Extraverts on the other hand get energized by social interaction.
(Social interaction requires a lot of processing.)
Why ? It may be related to an organism's baseline of arousal.
The idea is that extraverts may have a lower baseline arousal rate, that they enjoy raising by interacting socially.
Introverts have a high baseline level of arousal, which gets raised too far by too much social interaction.
It is thought that extraverts are the majority making up 85% of the population, and introverts 15%.
This would explain why open office plans are the norm.
Ironically introverts often self select for work that requires deep focus, and end up having to do it in open plan offices designed by extraverts who see nothing wrong with that.
This is a good book on the topic: https://www.amazon.ca/Quiet-Power-Introverts-World-Talking/d...
Three comments to address your question specifically:
1. Note the "more often" in the definition. It isn't "always". As such, sometimes introverts are energized by their social time.
2. Given the spectrum of extroversion and introversion, some folks may be less extreme and therefore exhibit less stereotypical behavior for their archetype.
3. Extreme introversion (or extroversion) is not perceived as being pathological until it "causes impairment in functioning and/or causes significant distress for the individual" [ibid]. This might be in the form of detachment that has some surface level similarities to being an extreme introvert, but is actually quite different.