The issue with platforms for istant messaging is that you really need your social circle to be there in order to use them. I use Nostr and SN to get in touxh with new people and ideas, but off course I cannot use them to get in touch with my close relatives, because they do not use them.

Matrix has the same issue, same for XMPP based messaging apps. If your social circle use it then okay, you're in a good spot. Otherwise you cannot really use that as your main messaging platform.

And for messaging platforms is really difficoult to convince people to use them...usually the usage of those kind of services is Paretian, meaning that people tend to do most of their messaging with 1/2 apps