That's a very good question. To be honest, I can only speculate. Speaking purely from my own experience I found that one commonality was that my stalkers were loners. I know not all loners are that way, but it was common to my experience with being stalked. They were all socially awkward and did not seem to be comfortable in group settings. It was a commonality that I was friendly. For most of my life I've been a friendly person and am generally happy. I've had a couple of times in my life where external events made me mistrust people up front, but I got past that. But, with my stalkers, each one said to me at one point something to the effect of, "you're the only girl who would give me the time of day." My nurturing instinct tends to get the better of me and I try to help people I feel are in need of help. In turn, some unhealthy people seem to be drawn to me. Also, in each of the instances, they misinterpreted human caring and kindness for romantic interest. Another common thing that was said to me was something to the effect of, they saw in me something they were lacking socially.

I have spent a lot of time in the South (US) and my upbringing was to be polite and respectful as well as caring and kind. Since I'm human, I fall short of this ideal and can be petty and nasty at times and was so as a teen. But, when I see someone hurting I honestly try to be supportive and helpful.

Again, that's a very good question and it would be interesting to see what some of the causes are for this.