I think that recent history clearly shows, that any larger organization and especially any public organization should at minimum also have a Mastodon representation. One can argue a lot on how a certain social network is superior to Mastodon. And often enough, that is indeed true. But all social networks that are run by a single entity are at the mercy of that entity. They might completely change their policies at a whim.

With Mastodon though, you can run your own instance. No one can take that from you and you can guarantee that your content is reachable for anyone interested. That should be reason enough to support it, even if you also have a presence on other networks.

In a sense, this reminds me of the old competition between the web and more centralized services like bulletin boards. The web is not as integrated, but its winning power was, that everyone can set up a web page, you are not dependent on any organization to do so, which could prevent you doing it.