It was almost universally considered by the German Reich and the men in charge of it that simply resting on their laurels, and their advanced technology for the remaining duration of the war would be an act of foolish hubris.
Sure, they had an overwhelming advantage in regards to arsenal when one was to look at what their enemies were fielding. However, Bruno's intervention in the timeline had not only helped Germany, but their rivals on the global stage as well.
Necessity was the mother of all invention, and a desperate nation could easily produce something of value based on what they witnessed their enemies using. The idea of fielding an old clunky machine like the British Mark I that was introduced in 1916 of Bruno's past life was absurd.