Free Software as a movement started by Richard Stallman and the FSF has inherent political and ideological goals.
Open Source was coined to contrast with this, and this term was endorsed by a lot of people working on open source software at that time, including Linus Torvalds.
So, the goal of open source software is not to change the world. The goal of open source software is to produce software that is open source. (The goals of "free software" are out of scope.)
Most things are worthless if not in service of something else. If you follow this line of thinking all the way to the end, then you just come to the useless conclusion that all life and everything we do is meaningless.
edit: This is not a very good response, it leaves too much unsaid. I'm basically just trying to conclude that most open source developers out there, at the very least, the long tail of them, are just writing code and working on things chiefly because they want to do so, with no particular expectations of anything in return. That doesn't mean they have zero goals or aspirations, but they are not the primary reason to do the work. And even without starting with such a goal, it doesn't mean nothing can be achieved, as one can see from projects like Linux, Krita, OBS and so forth. Clearly people don't write software in a vacuum for literally no reason at all, but OTOH whereas commercial software almost certainly has the explicit goal of "succeeding in the marketplace", there is no real inherent goal for open source software, and many people work on it without a stronger reason than "Because I want to."
