To try to stem the tide of the tremendous amount of unwanted animals that are born every year and then have to be euthanised due to lack of homes. In the US alone it is estimated that between 6-8 millions 'pets' are put down every year due to lack of space and homes. I cannot even imagine the number worldwide.
It hurts us more than it hurts them...lol
Getting a dog clipped is a way to eliminate agression and embarresing leg humping. It also serves to control his breeding should he get loose.
The same reason parents circumcise their beloved sons? And I can't understand that one either!