Signal Server has not seen updates for over 9 months. Moxie openly states that is not part of Signal's core values to support federation in the network.

IOW, even though they say they don't want to control your conversation, they do want you in their hands.

Moxie is not friendly towards such third party clients that connect to the main network. Also, I only used it as an example. There might be other reasons for a ban. The point is that you don't depend on them.