What is the reason for this difference?
The difference arises because the distance between two latitudes remains the same everywhere, resulting in the longer North-South distance of 3,214 km.
In contrast, the distance between two longitudes decreases as one moves towards the poles. Since India lies in the Northern Hemisphere, the meridians converge, causing the East-West distance to be shorter (2,933 km) despite the degree extent being roughly the same.
Explanation
The textbook explicitly states that the difference is based on the fact that the distance between two longitudes decreases towards the poles, whereas the distance between two latitudes remains the same everywhere. This explains why a 30-degree extent North-South yields 3,214 km, while a similar 30-degree extent East-West yields only 2,933 km.