Why do you think Arunachali tribes never advanced beyond agricultural rural forms of societies?

We are literally surrounded by so many cultures, plenty of which formed large confederacies and kingdoms which rivaled others on a large scale.

Our people had various tribal villages, clan unions and loose connections based on community. We weren't stone age or jungle-dwellers, but we didn't surpass the agricultural level and never built a single urban settlement. Hell, even now, who is the one building our towns?

I really wonder about this sometimes. Especially because we never even had a script. Some tribes like Monpas had a Kingdom, technically, though Monpas are considered nomadic pastoralists. Khamptis had a script and so did Singhphos but I can't remember them having kingdoms.

So what could be the reason we never had urban settlements like our neighbours and still remain rather backward compared to them? We may have fought with various polities and even won, but we didn't learn technology from them.