Google doesn't directly sell data in the first place - they leverage the data they have to improve the value of their ad network (in the form of enhanced targeting and attribution capabilities). It's actually in their best interest to _protect_ the data they have on you, as it's a primary competitive advantage they have over other ad networks.
As far as the unsavory interpretation of how they could conceivably use Fonts data to further that end: calls to download their fonts are another touchpoint with the Google ecosystem, and a theoretical vector for further tracking the browsing behavior and device graph of an individual.
That said, traditional font licensing for commercial use is absolutely bonkers[1][2][3]. Even if Google is using the data they collect from serving font files to feed into their user tracking, they've done a service to the web[4].
[1] https://designshack.net/articles/typography/what-is-a-font-l...
[2] Working at a creative agency, I learned that we can't so much as legally use a client-dictated (and licensed) font in a mockup without paying thousands of dollars for a license ourselves.
[3] Webfonts tend to be licensed on a per-pageview basis. One client got hit with a temporary flood of scraping/bot traffic, and the biggest economic impact was the unexpected six-figure font bill that month. We convinced them to put the site behind Cloudflare and used a Worker to strip out the font include for suspected bot traffic and inadvertently lowered their licensing cost by more than our annual retainer.
[4] I can't say how it is everywhere, but working at one of the top three marketing agencies, Google Fonts are the only approved open-source fonts we're allowed to use (since they're primarily free for commercial use, as well). Not every client is able or willing to absorb a 5-6 figure font line item for every engagement, so without Google Fonts we'd (and I presume other major agencies) would be stuck with using system default fonts everywhere.