( I know I am preaching to the choir when I quote you but this needs to be said )
Because he is convinced beyond any shadow of doubt whatsoever that he is in the right and you are in the wrong when it comes to cows ( or infact anything to do with Hinduism ). No amount of evidence of *ANY* kind is going to budge most Muslims EVEN the well educated ones!!
So far the one and only one Muslim that I have interacted with on this forum who gets it is
@DeadlyVenom .
Its a very eye opening experience to witness how doggedly they defend the indefensible.