1. A lot of text was rendered into PNGs, and that made the web less searchable, as well as less accessible, slower to load, and less mobile-friendly. All 4 of these factors do have economic impact at Google scale.
2. Fonts were one of the few features that Flash had that HTML5 was lacking, and we wanted to accelerate that transition. Again, mobile was one of the major driving factors.
3. For a while, we were organizationally funded under Google Docs. Again, fonts were one of the major missing features compared with Microsoft Office, so filling that gap was strategic. Here, our open source approach really paid off, otherwise dealing with proprietary font licensing in the context of documents that can be shared and copied would have been nightmarish.
4. To the extent that you are able to make the case that fonts make ads better (or advertisers happier), getting modest amounts of funding ceases to be a problem. To be clear, when I was on the team this was more of a glimmer of future abundant resources than day-to-day reality.
Lastly, while "charity" isn't exactly the right word, the motivations of the people working on the team are/were basically that we love fonts and want to make the Internet better. At Google scale, we were able to sell the project using basically a combination of the above arguments.
Never once when I was on the team were we asked to implement any form of individual user tracking, nor did I hear a suggestion of such a thing. All our work on collecting analytics was to improve performance and quantify our impact. I have no reason to believe things have changed on that front since I was directly involved.
I loved that site.