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 they can better control their own message, and can be sure that on their sites there won’t be something embarrassing to them right next to their posts.
Also, with Mastodon there is the advantage of a feed being able to be available as an RSS feed for those users who do not want to visit different sites individually (or even use a social media network).
I think, too, that with the W3C declaring ActivityPub protocol as a social network standard, this only helps give the Fediverse a better standing.