Because poeple do to get to their objective in the quickest possible time. It's boring and self imposed. Nobody is forced to do anything they don't want to. If you find what you are doing boring do something else.
Heh, he played a little trick. If he claims 'boring' is what defines grind, then there is no objective grind as 'boring' is a subjective appreciation of something. I'd find him a grind. Others may find life itself a grind, or the act of sitting down. It reduces it to a totallyt meaningless term, beyond providing him with a vehicle to spread more whining.