Blaming religion is not the answer. In fact Islam came to erase the practice of killing girls that was prominent in the region. Additionally, both Quran and Islamic teaching makes it very clear that killing any soul is a no no except for war or crimes.
So where this killing came from ? I am not sure but considering it exists in many countries and between religious and non-religious groups sugget it is something else. I would assume it is the tribal culture and poor living conditions.