I once developed a video game plugin for a niche flight simulator, that was subsequently bought by a few thousand people.
Their response left me flabbergasted: They thanked me! Personally, by email. They actually took out time of their own busy life to write a simple thank you note.
Never in my professional life have I experienced a response anything like this. Not as a researcher, being harassed and scolded by reviewers. Not as an embedded dev, by users or contractors being blissfully unaware of my existence. Not as an open source dev, hidden behind a pseudonym and fake "professionalism" in Github bug reports. The closest thing was perhaps professional recognition amongst colleagues.
I'd rather make a big personal impact on a small number of people than a small incremental impact on a large number of people. It's way more satisfying. Come to think of it, teaching and mentoring work similarly.