Are same-era military aircraft cockpits designed to be familiar to transitioning pilots?
Unless there is regulation enforcing certain aspects (e.g. as in the automotive sector), it is practicability would be the most probable cause leading to similar-ish cockpit designs.

Another reason would be convention, e.g. prior to the introduction of the side-stick, the center-stick was the way to do it.

Also, ergonomics is a very strong driver. During the landing approach, you wouldn't want to take your eyes far away from the windscreen to check altitude, speed and rate of sinking. Thus, these instruments are found in similar locations in most airplanes.