Most public matrix rooms were created by random people (unofficial) that just felt like "they should be here".

And the result is that there is no good activity in most of these places. Because there is no context for a real community. The rooms just exist in the ether.

Discord doesn't allow people to create public rooms without a context. Each "room" exists in a "house". The house has a clear owner. It has core family members. This is what creates good discourse and it's why public matrix rooms usually suck