Because all the grear powers wanted war. They thought war was inevatable to sort out rivalleries. Blaming the war just on those who lost the war, Germany, Austria-Hungary and the Ottoman Empire was toxic and wrong.

I think your viewing on the situation is a bit astray. If signing a treaty could've solved all the problems of early 20th century Europe, then there wouldn't of had to be a continental conflict. Germany wanted to exploit any international conflict it could for its own investment, however, Russia was a huge roadblock in the way of achieving this. By "this" I mean European hegemony. This is a pretty simple way of looking at it I believe if your a bit confused on how everything panned out, especially considering the amount of things that lead up to the outbreak of war