I'm not sure why it was decided that static Pages should not be categorized. On my site it would make absolute sense to be able to assign pages to categories. I have a lot of pages because I have a lot of static content.
I realized that I can assign a Page to a parent Page. But I don't need to be able to arrange the static content in a hierarchical way. Plus, this ability was added relatively recently and would require changes in my permalink structure. Several of my Pages have many outside sites linking to them, so this is a very undesirable change. I did add some parent pages, but this does not give me what I really need.
I think of it this way:
My site is like a book (work with me on this). The book has chapters that are defined by categories. It has an index that is defined by tags. Then it has this other stuff that has to sit in the appendix because I can't add it to a chapters, even though it rightly belongs in either a chapter with other content or its own chapter. It's not easily arranged in a hierarchical way, so it's hard to present it in any logical fashion that would make it easy for readers to find. I can't even add it to the index - yes I know I can do this via a plugin - so readers can't even find it there.
There's no rule that says that categories have to be used on pages. But they should be available for those using WP as a CMS who need them. If you agree, please go over to this Idea and vote.