I think by 1917 it was finally dawning on the Germans that invading "deep" Russia was a waste of time. The logistics required to drive far beyond the front line in a "Moscow or bust!" move were beyond the Eastern Command and, as others have said, the Italian and Western Fronts were more important to make progress on.
After the Brusilov offensive has slackened off, there was practically no movement on the Eastern front in 1917 and the Germans were happy with it staying that way.
EDIT: Sorry, re-read the OP to see it's after the Kerensky Offensive. It would be a massacre with potentially hundreds of thousands of Russians being captured or killed (mainly captured of course) but my point about the logistics and the primacy of the Italian and Western Fronts still stand, I believe.