That is a darn good question,and why does discrimination exist period in anything,my answer would be it is the mind set of the people and the leader to lead the people to think in a box type fashion and never deviate from what they have been told,never use your own mind and think outside the box,that is one reason why each of us should have our own personal relationship with God it is nice for someone to pray for you but they can't do it better than you can because God would like to hear from you,just you and him,you don't need a crowd,it is nice to worship from time to time with a congregation because the more prayers go up the more blessings come down,but to think your religion it the know all and end all religion,it not how God would want it,each time you research anyone's religion you will find god to be in the image of the person to whom the religion belongs...good luck
Because most religious texts and traditions claim their religion is the only true religion, the only way to salvation, the only way to god, all others are wrong, all others are evil, all followers of other religions are doomed. With that kind of thinking there isn't much room for compassion.