Why must prices increase when supply is short?

In the study of micro economics, we are taught that when supply to of  goods is short prices of those goods increase. The question is why is there a price increase?

As I pondered about the increase in prices I couldn't find an observable and valid reason. Until I realised that the true reason is pure GREED. Since the supply is short but the demand is high, why not extort consumers into paying high prices until there is an abundant supply and prices can be lowered. In monopolistic competition where there is more than one supplier or manufacturer, the tendency to lower prices when abundant supply arrives will be that each manufacturer or supplier will be compelled to lower prices because their rivals will lower their prices to sell more of their products.

The supply of goods can face shortfalls in supply to many reasons. There could be strikes which cut production. There can be trade embargoes that cause shortages of goods. Thus suppliers can hike prices to earn excessive profits from shortfalls in supply. 

In conclusion, the reason for price increases when there is a shortfall in supply is pure greed. When suppliers want to maximise profits a shortage of supply is god send to them. But this will bring misery to consumers.