Well from a genetic standpoint they want you dead so your suffering isn't that big of a deal to them, for the sadist types its actually funny and rewarding to them. There was a study that showed women take out their dating frustrations on men they deem inferior to them or their previous partner. So they are likely seeking to inflict harm when given the opportunity and if you look like a push over it only increases the chances they'll be a bitch, it improves their self esteem.