And for programmers that aren't hackers, they just appreciate the practical upsides of having mature humans that can take accountability for decisions that affect your work as coworkers.
It is, but it is largely also single-player.
People are people, all different, some hackers enjoy the solitude of doing their project by themselves with no human interaction whatsoever, others enjoy and thrive with a collaborative setting, spitting ideas, showing code, and getting feedback to iterate on and improve them.
I've belonged to the latter camp most of my life even though I acted like the first when I was learning how to program (and on my first job); I'm not a stereotypical extrovert but love nerding about stuff together with someone: coding an idea, making music, working on wood, for me those are all more enjoyable with another human sharing the same passion.
Even those that have less bandwidth for human interaction value being in the loop.
This exists on a spectrum for both interactor and interactee: some folks are more introverted than others, some folks don't mind talking shop with fellow hackers but don't want to get into business-y stuff with PMs.
There may be reasons other than self promotion