Nordic model is a way of implementing "sex work is bad and should be illegal". Whether it's implemented in the Nordic model way, or in the "let's jail sex workers!" way does not matter that much - it's still a morality based law (on the idea that sex is sinful I guess) that puts a whole class of workers to illegality.
Germany's approach is it's not. That you can have sex for money if you want to.
So if you think that sex workers shouldn't exist, of course Germany's approach "does not work".
But if you don't think that sex work is amoral, then Nordic model just oppresses an already marginalized group. For me, that is what does not work.
Fighting human trafficking and abuse is of course necessary, but doing it by hurting already vulnerable and marginalized people makes it hard to believe that you're actually interested in helping, instead of enforcing morality where sex is sinful.
All I know is that Germany's way did not work out. Trafficking and forced prostitution are a huge problem and the police has to deal with controlling legal brothels and fighting against illegal forms of prostitution.