Paul, the Germany Project decided not to maintain historic categories, simply because it is actually contrary to what a category is for. If you group your people all in the Bad Iburg category (as you seem to do), it is easier to see over time with how many people you are related. The Fürstbistum Osnabrück does not belong to those areas which changed their name or territory seemingly every five years. But there are towns in Germany where the territory they were administered from changed really often.
Just as example the history of Bockenheim an der Weinstraße only in the 20th century (taken from the German Wikipedia): There were Großbockenheim and Kleinbockenheim. Already in the 1920s there were people lobbying for a fusion of the two villages. In 1947 there was a ballot if they should be unified. No. Next ballot in 1955, this time yes. Unification on 1 Jan 1956. Bockenheim, as it was named then, was put into the Landkreis Frankenthal. In 1969, there was a big administrative reform in Rheinland-Pfalz, they got part of the Landkreis Bad Dürkheim. In 1972, there was a new reform on the lower administrative level, and they got part of the Verbandsgemeinde Grünstadt-Land, which in 2018 was dissolved and joined the Verbandsgemeinde Leiningerland.
Now, if every historical entity got their own category, you'd have a zillion category with only one person in it, because for the next generation the category would not fit anymore. So this is (one of) the reason(s) why we categorize it only in the modern way.
