I think the perfect answer will tend to be a psychological one.The question is whether some people have any empathy for the life of humans at all.If they don't,then they will not care to stamp it out on their way to accumulating one of the most important elements of material life.
Now why they don't have that empathy for others? I think it's hidden somewhere in their education and upbringing.
Recent findings in neurological science confirms that humans,by nature,are empathetic beings.It's later in life that they are taught and encouraged to be insensitive.
Implementing new laws,or forceful means will not cure this tendency.We must redefine the way we teach people into a holistic activity.