"Why?" The sad answer is "Because they can." That's how predators operate. They look for weakness and then exploit it for their own selfish, perverted pleasure. Often times these same people are damaged in some way as well. Example: WARNING: EXTREME TRIGGER RISK :
Also, sometimes it's as if there is no answer. My other personalities and I have adopted a saying recently that we say to each other at times like this. "Why is the sky blue?"