"If we were able to do it here why on earth not in Germany?"
I've only visited two markets locally in Berlin this year and neither of them seemed to have extra security in the way of concrete barriers stopping this kind of lorry attack from happening. Most markets are also freely accessible with no entry and exit points, and no security checking bags. I noticed that contrasted hugely with a fair I went to in Monaco last month - this kind of attack simply couldn't have happened there. I suspect part of it is financial - Berlin is broke. Another problem is that many cities have one huge Xmas market in the city centre, which is often pedestrianised - but Berlin has loads of smaller markets all over the place, every district has one or two, and it would be impossible to seal off the areas entirely. breitscheid Platz, where this happened, is a thin strip of pedstrianised area where the church is located, but left and right of it there are important roads which would really knacker the traffic flow if they were closed off. It would be impossible to close off major roads adjoining every market in Berlin. So I don't know what the solution is.