Perhaps it has something to do with "putting one's best foot forward" being part of the natural domain of the deceptive person. The nice guy may also appear a bit uncomfortable whereas the more sociopathic person will tend to come across as more comfortable and therefore be perceived as more sincere.
I don’t think my beloved King of Kool - Steve McQueen - a bad boy if ever there was one - was a sociopath. Actually, a patriotic Republican who simply couldn’t handle all that success with money, wine and women. I think women are attracted to dynamic men when they are young.