Banned from Australia? Well the governments tolerate abusive cults and neo-Nazis. The NSN hasn't yet made it onto the official terrorist organisations list over here. (No, I'm not exaggerating when I say 'cult')

Or if you meant banned from the event: it's because they were heavily involved in organising it in every state, they're effectively running the rally as a front. They're not going to ban themselves from their own rally. Mainstream outlets like ABC and The Age summarised this before the rallies, journalist Tom Tanuki has made in-depth videos detailing the evidence.

Bevase they're not protesting Climate change.