From reading reddit, I learned that a large part was also how it simplified things. Here in the north it’s pretty straightforward, but as you can see on this map [0] it gets slightly more confusing in large parts of Germany.
edit: Just to explain how the north is even simpler than it looks, VGSF is not relevant and simply included in NAH.SH, and HVV has a tight cooperation with NAH.SH, so it’s often just one ticket for Hamburg and Schleswig-Holstein.
[0]: https://en.wikipedia.org/wiki/List_of_German_transport_assoc...
edit: Just to explain how the north is even simpler than it looks, VGSF is not relevant and simply included in NAH.SH, and HVV has a tight cooperation with NAH.SH, so it’s often just one ticket for Hamburg and Schleswig-Holstein.