[adrianba]

I don't know about German law specifically, but damages can be shown in a variety of ways. In the US, courts have recognized publishers of open-source software as receiving value from having made source code available at no charge, such as reputational gain or adoption leading to future sales of related products or services.

[chippiewill]

Additionally the possibility to relicense the software to the offender under commercial terms and gain direct monetary value.

Presumably it's important to establish damages (at least in a US jurisdiction) because otherwise they wouldn't have standing to bring a lawsuit.