Which is a bit silly, but more a theoretical problem, right? I'd assume (I can't actually find a map of the coverage), that people for whom a BC 100 makes sense travel mostly by train, thus live near a train station with a good connection. Which will then be in one of the 130 cities that include the public transport with the City Ticket.
Everybody I know who has a Bahncard 100 uses it for commuting. While they generally live "close" to a train station they need public transport on both ends of the journey and buy additional tickets, e.g. another ~60€/month for a Berlin ticket.
