I don't know about you but I'm speaking from experience, not hypothetically. I shared multiple open source side projects where I made something for myself then shared it with the world.

> Typically they expect to get something out of it that they don’t get by their project just sitting on GitHub.

Can you expand? the vast majority of open source projects don't make a dime. I don't see the ulterior motive you're talking about. Unless you mean like they get more GitHub stars?

> Typically they expect to get something out of it that

Where do I begin ?

Satisfaction, narcissism, sense of self-worth, approval, love they never got from their parents…