Introversion can be a byproduct of so many different things that saying “it’s just a label” is not only absurd by itself, but utterly disrespectful too. It can be a choice too, sure, but that’s not the case for quite a lot of people.
I do care about what values, passions and friends I have, and I have tried to find a set that is consistent.
I do not mind if someone tells me "I am an introvert", even if I do not find it extremely interesting. But if he says "I am introvert and will be unhappy all my life because I can't change that", I can't avoid thinking that he is focusing on something that does not help.
Knowing you are an introvert (aka labelling it) can help you realise what works for you and what are your boundaries.
The point is that introversion does not mean complete isolation—this is the bit every extrovert neurotypical person in this thread seems unable grasp in the slightest.
“Prefers to be alone” does not mean “cannot function socially”.
The problem is lots of people put this label on themselves without knowing for sure that it's the case, thus setting boundaries that don't need to exist.
So do I, but when one attempts to push a square peg through a round hole (and sufficient force applied), the structural integrity of the square peg is compromised.
This is to say, if working against your inertia becomes traumatically painful, you may in reality be working against your nature rather than your inertia.
It requires a certain wisdom and a great deal of experience to distinguish between those aspects of oneself are immutable vs mutable. But I believe firmly that a loosely-held understanding of one's immutable nature is highly useful in living a happy life. I consider it equally important to what you are getting at: that some aspects which appear to be immutable are actually not, and the only way to know for sure is to stretch outside of one's comfort zone.
It takes skill and experience to tell the difference, but the effort is worth it.
We should take every opportunity to make life as fulfilling as possible, even if we don't always succeed due to things outside of our control. (Note: this is an abstract claim for what you want, I'm not saying being extroverted is more fulfilling than being an introvert.)
Certainly, what you find comfortable is somewhat choosey. Over time it changes and evolves, from your own experiences. The more you do things, the easier and more comfortable they become.
People are different. Just accept it.