I don't think they have the wording so they can be random or arbitrary, but I do think that the vague terminology like "not limited to" and "other items we determine may be harmful and disruptive" is there so they can prohibit items without notice. It gives them a fallback when new items are added (and the website is not yet updated) or to use their discretion about banning an items that isn't explicitly mentioned on the list. That way, if someone were to complain that the items they wanted to bring into the parks wasn't on the list, Guest Services or the Security CM can say that they can prohibit any item deemed potentially harmful or disruptive and that the list isn't meant to be exhaustive. I think that can appear random or arbitrary to the guests, but hopefully the Security CMs are ultimately just following the company-specified guidelines.