Programming culture selects for those people, to an extent.

If you're employed as a programmer, you're most likely being paid to solve other people's problems by writing code. If you can't communicate with those people, you'll never be able to do that successfully.

It's no conspiracy. A socially clueless introvert who's being paid a lot of money to do nothing useful doesn't have much to offer.

Of course you have to communicate with people to be effective.

There are also a lot of tasks where thinking deeply without distractions or interruptions for an extended period of time is the best way to come up with good solutions.

And even a lot of the best communication comes from taking time in quiet and deeply thinking about what you want to say and writing a good, convincing argument.

Thinking introverts have nothing productive to offer is just bigotry, and really makes you come across as a complete ass.

Of course you sometimes need quiet time alone to work on a programming task. The point is that you'd better also be capable of communicating frequently and effectively with your colleagues. For sure, many introverts are perfectly capable of doing that. (There are also many extroverts who can work alone when the occasion calls for it.) My point is that introversion is not a wholly adventitious trait for a programmer. Looking at the job description objectively, one would not expect programmers to skew strongly towards introversion.