I believe the idea is the motivate you to contribute further by proving that your edit made a difference. How does your edit being viewed 100 thousand times makes you less interested in contributing? Would you rather contribute to a product nobody uses?

> I thought "why am I contributing to this ad-powered product that they're monetizing for millions, for free?"

You already knew Google Maps was monetized by ads, before making an edit.

I don't think it's fair to see this as free labor for Google. Your edits to Google Maps could be related to your own business. Or you might be helping your favorite local business to get more visibility and customers.

Perhaps it can also be seen as a contribution to your neighborhood.