There is more than one reason for that. First, I have a greater knowledge of (and greater interest in) regions where my ancestors and I have lived. Finally, the web site is always a work in progress; and, it is possible that certain pages have not yet been added, simply because I haven't gotten around to writing them yet.
The primary reason is that local histories (counties and towns) are emphasized more at this site. The reason for this is that the histories at the national or state level have probably already been covered by other web sites. Meanwhile, the histories at a more local level are often the ones most neglected; and, this web site will attempt to fill that niche.
The national and state histories will be updated whenever time and availability of information permit. As was mentioned, national and state histories are not the highest priority of this web site.
Those would be Union County, South Dakota and the town of Beresford, South Dakota.
The web site should always be considered a work in progress; and by its nature, the content of this web site will probably never be completely finished. Also, my first priority is my genealogical research; and, this history web site is merely a spinoff of my genealogical research. Finally, I do have a day job; so, I have to spend a some of my time working to pay my bills, even if it takes away from my research time.