Early military planes were primarily designed for observational purposes. By having the piolet in the back the passenger (observer) would have the best possible view.

As a matter of fact in early aircraft in Germany the passenger would be a officer and the pilot would be a lower rank and their job was essentially to chauffeur the officer around.

The positioning of the two seats is designed to balance the aircraft and prevent it from becoming too nose heavy. (It is designed to be slightly nose heavy.