Anthony Beevor
Entire books have been written about this subject (as well as about the rape commited by Western allies not only in Germany but also the liberated countries, which happened but in a much smaller scale).
If I remember correctly there are 3 main reasons why discussions about this only happened recently.
1. It was politically inconvenient, (in the West) and often outright discouraged if not banned (in the East) to talk about the crimes of the now allied countries.
2. Societies were much more conservative back then and often engaged in victim-blaming (Novi gave a perfect example for this above "They did it for food".)
3. As a consequence of 1 +2 and due to shame and a wish to forget the victims only spoke about this mqny decades later, a pattern common in victims of sexual assault.