Well, the title is a lie, that's what. In the frame of this novel, nothing is ever quiet on the Front – unless it's dead. And the war took a long time to die.
That Front is the front lines of the battle between Germany and mostly the British and French during World War I. There were a few fronts along which battles were being fought – this was just the western one, implying that this is a story that played out on several fronts. We have one little view into one little story on one little set of Prussian hills.
The historical foreword to the book by Harry Hansen details the historical events, citing newsreel posts from Germany and France as the war ground along. To calm the masses, a regular refrain from the journalist community – co-opted by government naysayers – was that "all was quiet." But in fact, as the reader pores through these jagged, sparse pages of All Quiet the Front is anything but quiet.
You'll also notice that the words of this title appear in the final moment of the novel. And how ironic is it that our protagonist dies when things are quiet? He survives many loud and chaotic battles, but dies on a day that is "all quiet." (You can read more about Paul's death in "What's Up with the Ending?")
In German the title of this novel is Im Westen nichts Neues, which literally translates to In the West Nothing New (source). How does this title change your understanding of the novel? Which title do you prefer?