Gender bias is a very important aspect. According to BAMF numbers up to Dec 2015 , taking only people that may be now or soon looking for a partner. Even looking at people ages 16-30 only, BAMF data (which are conservative, just above 400k altogether) identify at least 113,000 “missing girls/women” (difference between men and women within that age range). In the same age range, the share of men is 78.62 percent.
This is probably unprecedented, and it is something that should be a very high priority for politicians.