A) A hub further south than Berlin. If Dresden (end station for the line) was a "hub" then OK B) Hard to find and find intercomnnectimg routes. C) It departures from Copenhagen South not Copenhagen Central. D) Poor availability. You need to book in advance if you're not very flexible on dates. This compounds when you need to interconnected. E) Insane prices. They have optimized themselves out of business. CPH - Berlin in a private cabin for 2 will cost around USD $500. This much more expensive than plane tickets and a very nice hotel room.

If you talk with "regular" people this does not even register as an option. Hence a poor network is not comparable to a proper network. It needs to be able to compete - not on all parameters but at least some.