What potential has China seen in Pakistan, that the rest of the world haven't seen, that urges China to continuously invest in billions?

akistan surely provides a lot of advantages to China, starting from able to supply raw materials, serving as a market, and the means to connect Chinese production facilities to the west (mainly Persian gulf).

However, there is more than one reason why Pakistan is the best choice for China’s requirements such as:

Pakistan’s Geographic position
Pakistan’s desperate economic situation
Pakistan - Army with a Nation
Pakistan’s obsession with Kashmir and India
Finally Client or Colonial relationships
Pakistan’s Geographic position: Pakistan’s Geo geography is obvious for anyone to see, as given in the below picture it saves China about 30–35 days of shipping which means rapid access to goods and dispatching of finished products and at a much lower transportation cost.