Why do voltage source are short circuited while current source are open circuited??

They are only words. You turn off a light switch by opening the circuit; it doesn't matter if you have a current source or a voltage source.

'Circuit' means a circle. Electricity has to flow from its source and return to its source. Voltage refers to a force between the source and the return, current is a flow of charge. Here is a free course in the basics:
www.phy.davidson.edu/instrumentation/NEETS.htm