I'd expect the 4k option for all of germany to be less popular (in % of ticket holders/population) due to pure odds (aka chances are high an average person won't regularly need to journey from hamburg to munich, but they might regularly journey somewhere inside their Bundesland. so it's less likely it's "worth it" for people?
In the city centre near Goetheplatz I had... drumm roll. EDGE. 2.5G
In July 2023.
This is the home of DE-CIX, the European continents largest internet exchange.
> It's a great peace of mind to just hop onto any bus/tram/train in the country and not have to worry about tickets
It's like with theme parks: I prefer paying one big sum at the start and then getting to enjoy myself for the whole day over being nickle-and-dimed at every ride.
I don't do it very often, but I've more than once visited other cities in the area on a whim because the marginal cost is zero. That specialty shop in another city 400 kilometers away? Suddenly within reach, if the only cost to get there is time. And being on a train instead of driving a car means I can work while getting there and back.
And then there's the other perks of the BC100 that make travelling generally more chilled: Large stations have frequent-travelers' lounges with free drinks and working spaces. On long-distance trains, there's a section of the train (usually a quarter of a railcar) that's reserved for frequent travellers and BC100 owners, so I don't have to worry about seat reservations even when the trains are crowded. The purchase price for a 2nd-class BC100 also gives enough bonus points for 8-9 free upgrades to First Class per year; I use those when I know I'll be going for a particularly long distance.
I went to uni in Cologne and a lot of banker types who would daily commute from Cologne to Frankfurt always had one. Very popular with business people doing these mid-range round trips. For regular travelers too expensive though.