I had some flights with Lufthansa from Istanbul (IST) to Munich (MUC) about 2 years ago. There were several flights a day, but there isn't any for a while.
Why did Lufthansa stop flying between Istanbul and Munich? Is there any announcement for it?
I have found an answer on CNN Türk.
It seems that Lufthansa cancelled flights not only from Istanbul, but also from Ankara and Izmir due to low demand. In April 2017, Izmir-Munich flights restarted. According to Lufthansa Turkey General Manager Kemal Geçer, Istanbul-Munich and Ankara-Munich flights also will restart as soon as the demand recovers.
Extra information: The number of German visitors decreased 27.6% in 2016 compared to 2015. The border stats show that the number already started to recover, for example 10.8% up in June 2017 compared to June 2016.