Lighting in those areas, which tend to be dark or populated, helps folks feel safer. Taking away the ads makes these places darker, and I can understand not suddenly having nervous folks not take the bus or train.
Though, I agree: They can get bent about the contracts. The proper response is to install proper lighting without the ads. Hopefully this is in the works.
Which really isn't so surprising, considering how pervasive advertising is in many societies.
Like you said, other advertisers would probably happily replace them and even if that's not the case I think a country as wealthy as Germany should be able to find some way to finance bus stops ;-)
Unless I'm completely blanking on these signs being used elsewhere, excluding the bus-stop signs sounds like this will not have any noticeable effect apart from providing a nice sounding headline.
yes, I also did not notice any of those here in Hamburg. there is a smaller one in Harvestehude; even those are so rare that I clearly noticed this one.