This is a map of German public transit companies: [0]. I've heard the current fractured system be compared to the Holy Roman Empire. Every little region has its own ticketing system. If you arrive in a new city, you have to figure out how to buy local transit tickets, often with quite complicated rules (e.g., "Is my destination in zone 1, 2, 3 or 4 of this city, and what zone am I in now?"). You can usually buy monthly cards for an individual transit company, but what if you live in one region and work in another? You may have to buy two separate monthly tickets. It's a mess.
With the new system, you just buy one monthly ticket, and you can ride on local transit anywhere in Germany. There's no more worrying about different ticketing systems, if city X is in transit region Y, and so on.
The fact that the new monthly ticket is half the price of what a typical monthly transit ticket used to cost is just the icing on top of the cake.
I should also mention that while this solves one problem with the transit system in Germany, there's another, much larger problem that is still unsolved: on-time performance is abysmal, after years of neglected maintenance. The Deutsche Bahn is not what it used to be.
0. https://upload.wikimedia.org/wikipedia/commons/f/f3/Karte_de...