This is Germany we're talking about, right? Something like half the population already speaks English to some degree and that is specifically concentrated in the part of the country that is already highly educated and would be working with those immigrants.

Educated immigrants often consider countries interchangeable. They are in a country, because they found an opportunity and took it. But they are not committed to stay, because better opportunities could arise elsewhere. When you have already immigrated once, doing it again is only going to get easier.

Immigrants with fewer opportunities are more likely to try to learn the language and integrate. When a country is offering them something they can't find anywhere else, it makes more sense to go through all that effort. Even knowing that they will probably never fully fit in.