Some people feel very little compassion towards animals. A lot of people, however, do feel compassion, but they are simply unaware (or don't want to think about) how animals are killed for food - the actual moments leading up to the killing and the death itself. They don't visualize the process of killing a cow, pig, etc - the screams, the blood, etc. If more people witnessed the killing process, the percentage of vegetarians would most likely increase.