The most confusing part to me is that the option is controlled by the category page layout, it does make sense as a category setting though… I think if we limited the scope by default we’d have to make the other categories searchable at least?
I did just find a post where someone was confused about an incomplete list: https://meta.discourse.org/t/not-able-to-change-category-if-i-start-a-new-topic-from-a-specific-category/46889/17?u=awesomerobot