The safety of Germany's borders might be a demand of Germany's neighbors. Germany can import all the Muslims it wants. But Netherlands, Poland, France, Austria (and any I left out) should be able to keep them inside Germany.
The pay, retirement after about 20 years, power / ability to intimidate people, love of action and excitement. The first two are explicitly advertised to recruit people to NYPD. Oh yeah helping people too. Every profession is supposed to be all about helping people. They're all saints in those professions.