Non-voters are a diverse group, there's no singular reason why people don't vote. Trying to paint all non-voters as people who've lost faith in politics is utter nonsense.
People in Germany are generally satisfied with both the state of their democracy and their individual lifes, that's just how it is.
Grand total of 6% aren't "satisfied at all" with the state of German democracy, 73% are satisfied.
https://de.statista.com/statistik/d...riedenheit-mit-der-demokratie-in-deutschland/
There's a huge difference between east and west, though. 77% satisfied in the west, just 47% in the east (59% previously, the huge drop can likely be attributed to the refugee topic).
http://m.bpb.de/nachschlagen/datenreport-2016/226945/zufriedenheit-mit-der-demokratie
According to Pew Research 86% of Germans regard the economy as good, the second highest value in the poll.
http://www.pewglobal.org/2017/06/05/global-publics-more-upbeat-about-the-economy/
According to the DIW life satisfication in Germany is currently the highest in 25 years.
http://m.spiegel.de/wirtschaft/sozi...nie-seit-der-wiedervereinigung-a-1139233.html