Sure, I expect Google is slurping all of my connections to help build an ad profile on me. But what about the other companies? They've got to keep the lights on somehow.
Google says they don't - from https://developers.google.com/speed/public-dns/privacy:
> We don't correlate or combine information from our temporary or permanent logs with any personal information that you have provided Google for other services.
Honestly, Google DNS policy seems largely similar to Cloudflare, with the exception of 3rd party audit.
Cloudfare apparently doesn't do GeoIP mapping, so, till they implement that, it's not going to be useful for me.
tl;dr: These companies are successful when more people use the Internet. DNS is a major contributor to poor perceived internet performance. Thus providing better DNS services encourages people to use the Internet more.