I'm not sure I'd ever be motivated to provide a logical explanation to its appeal

No, there isn't one, but then there isn't really a 'logical explanation' for the appeal of snooker or stamp collecting or any number of pastimes people indulge in. You either find something interesting and enjoyable or you don't. The slash side of slash...*shrugs* definitely not something you can explain if people don't see it. People have all sorts of different explanations for why people are into slash, but really there isn't a single slash-type person so no one theory would cover it.