The way WikiTree was built (or any other wiki style site really), all of the namespaces are generally treated as public facing. Each of the namespaces (Person profiles, categories, help, templates, space pages, etc.) work both independently, and as support for other pages. Since they can be independent pages, they have been made available to be indexed by web crawlers.
As an example, we have shipping categories. These categories contain some data and links to profiles that may be of interest to an web searcher, but the category may not have a supporting help, project or space page. Should we hide the category from searches?
There was a problem with heavy editing of one of the Scottish Clans categories last year from someone who appeared to have joined WT in order to add blogger style content to that particular category page, the situation was quickly taken in hand by an observant ranger and the hacker quietly blocked.
This is inevitable. Many wiki sites suffer this same type of vandalism, which is why WikiTree has specialized members and projects created to monitor and protect the site.