I think its more just an accident of history - lisp became popular, prolog faded. Sometimes some technologies just happen to fade out due to chance.

I have heard, that people who have never programmed before often have an easier time learning prolog than people who have, so I think there's an element of forgetting what you already know. When I had to learn it for school, there was this book of small puzzles (Sort of like the little lisper but for prolog) that was really helpful, but I can't remember the name of it.