Emotionally unavailable....

I've always trusted this site for some sound advice. Some are nasty. Why are we attracted to emotionally unavailable men? I've written many times about my FWB turned BFF. His new girlfriend (8 months) is the same. Emotionally unavailable. Why would he be attracted to someone with no emotion when he could be with someone who has shown him nothing but empathy and been sympathetic? Am I too nice? I'm not getting in between them. Just so fucking curious!