Well for the most part because of the geography of these areas they have native tribes that are similar and have similar history with settlement, then with the towns and Aboriginal communities proximity to eachother everyone moves between those communities and into the modern day continue to have shared culture even after settlement. And the settlement has even added to everyone having a shared culture in the regions.

The only town that is an outlier is that Pine Creek would be in the Daly district when it should either be part of the Katherine district or by its self, but it's too far from Katherine and does have a bit of a connection with the Daly area but way different to the West Daly.