Why was my footbal (soccer) team transferred to another division?
As far as I could see the reason is the same as the one in real life/football: - divisions should have similar number of teams - teams should be allocated to divisions according to geographical positions
So for example if in one year your IV.6 was having too many teams, some are distributed to other divisions which are closer to them (geographically).
The reason behind this is to reduce the cost of travelling for small clubs.