Why migrants come to Germany for work and then leave again

Germany has long attracted skilled workers to its labor market. The country has been much less successful at retaining them. So what is Germany doing wrong?

source https://www.dw.com/en/why-migrants-come-to-germany-for-work-and-then-leave-again/a-77853162?maca=en-rss-en-ger-1023-rdf