What is the main reason for the increase of foreign immigrants in Germany?

Now, because Germany's population is aging and the labor force is insufficient, it needs to be supplemented by foreign population, so the policy is relatively loose.

Attract foreign students to study in Germany and encourage them to stay in Germany.

There are also high welfare and high income living conditions in Germany. After all, it is the strongest country in Europe, attracting foreign population.

Some Turks and Russians stayed in Germany because of World War II, and their descendants also immigrated. This is also a reason. Of course, this refers to the last century.