There *was* a German resistance movement. It was small, and the government was very effective at infiltrating it and quashing it. But there was resistance, there were attempts on Hitler's life, remember.
I'll have to go look to get exact details, but one of my students did a research project on the resistance movement and found that there were two problems: the Nazis were effective at quashing it and the movement was ineffective at getting outside help (the Americans, for example, gave it almost no help at all).
Elizabeth