This is certainly a growing trend which was first started amongst end-users themselves, and slowly we've seen a few news media outlets also following suite. So far, only a very few government agencies have actually followed. Coming to mind are also The Netherlands. What is attractive for many organisations and agencies on Mastodon, is that...
Germany seems to have been an earlier adopter of Mastodon (the instance is hosted by the government). If I understood it correctly they just decided to stop using Twitter, it’s not like they started the instance today.