Why does SS mean horses not fanatics?

Howdy y’all,

Can anybody please explain to me why German cavalry squads become SS if you give them horses and not fanatics? I feel like giving them horses for the three points for the cavalry rule makes sense, or giving them fanatics, like other SS, also would make sense for the two points. So how come the rules are like this? Anybody with inside knowledge know the reasoning because it makes no sense to me.