Programming is often a team effort for introverts. When working as a developer, you will run into decisions other developers have made that you consider mistakes.
It could be a data structure designed with three tightly bound tables. It could be a massive REST API managing all the company's requests with obsolete technology you need to extend or replace. It could include delicate, untested code that when modified, is likely to cause both personal and technical explosion.
I have built systems that contained all of these flaws, or worked with the (sometimes catastrophic) results. Working with and learning from other programmers is simply easier when you can critique their code effectively without offending them.