Apparently, when a request pattern is mapped to a method via the @RequestMapping annotation, it is mapped to to the concrete method implementation. So a request that matches the declaration will invoke GoalServiceImpl.removeGoal() directly rather than the method that originally declared the @RequestMapping ie GoalService.removeGoal().
Since an annotation on an interface, interface method, or interface method parameter does not carry over to the implementation there is no way for Spring MVC to recognize this as a @PathVariable unless the implementing class declares it explicitly. Without it, any AOP advice that targets @PathVariable parameters will not be executed.