What these Indian's cannot fathom for some weird reason is that Indus Valley is entirely distinct from Ganga Basin and Dravid India. Indus Valley is essentially complete desert [Jacobabad in Sindh is one of the driest and hottest places on earth] to semi- arid desert with high atitude cold desert in the periphery. Through it the River Indus flows and only within the flood basin which only extends to few mile ribbon was irrigation possible until modern engineering was introduced by British. Up till then agriculture that could support population was strictly limited along the rivers which thread through the region. Only in the extreme north west and north in the shadow of the mountains does rain become just about sufficient. In this region a semi-nomadic pastoral culture persisted asides from the narrow ribbon along the Indus tributery rivers.
Compare this with the humid, high rain, damp climate in most of the Ganga basin which can support massive, dense poulations and which was thick jungle before.
The satellite image below lays bare the points I made. Along the Indus in Pakistan the British era irrigation which extended the narrow ribbon to a wider irrigated zone is visible but even then desert is biting it at the edges.
Rainfall map of South Asia, Notice most of Pakistan is desert with under 5 inches of precipitation. For instance Karachi has climate similar to Cairo or Baghdad.
Geography and history are my passions. And I have good knowledge of Pakistani geography. OPen another thread and I can teach you if you want. Did you know that semi arid desert begins just south of Lahore? And you know Lahore is well to the north of Punjab.
No doubt Indian history books singing songs about 'Mauryas'?