In the words of ZZ Top "every girls crazy for a sharped dressed man".
I think it is just for the fact that everyone knows the name ss and assume that they all were fanatical super human, allies crushing machines who were never defeated. Plus it's weird because I don't really associate Germans with fashion, but it's hard to say anyone else had cooler uniforms than the ss. Plus the word ss is cool, like Camero SS, it's just cool.
Just like people like playing grand theft auto, it feels good to be bad sometimes.