The impression I have is that Germans are bigger users of the Fediverse in general than other countries, as in statistically overrepresented. Mastodon is originally a German project. Germans also created a Fediverse application for buying and selling second-hand items, Flohmarkt (Flea Market). Some other posts here have mentioned that Germans are culturally/historically more interested in privacy than many others, which may help explain the interest in the Fediverse. Finally, Lemmy is also an European project, so it makes sense that there would be more Europeans here, and Germany is the largest European economy and the most populous Western-European nation. Those are all probably factors contributing to this.