I don't know why people use fonts served from Google on their websites. Just serve the fonts from the server the site is on. It's like having javascript libraries served by 3rd parties; it's less robust.
I guess one advantage could be to better use browser caches for these things? If you visit multiple websites that include the same fonts or javascript libraries, the browser can reuse the cache for them.
Nowadays, cache is partitioned by website (https://developers.google.com/web/updates/2020/10/http-cache...)