dude looking at your parents with a smile give you the reward of a hajj (each time you look at them) why pray ishraq?? on a serious note it is becaue we love makkah and medina so much thats why we go for umrah.. it is some thing that you can be felt only not discussed. you will get your answer once you go for hajj or umrah. InshAllah. 
I heard a saying of Hazrat Ali (ra) which goes some thing like this; i pray to Allah not because of the reward i am going to get in return but because it is His right to be prayed to in a good manner.