The consolidation in aerospace and defense was a much longer process than that. All of the companies with names like “McDonnell Douglas”, “Lockheed Martin”, or “Northrop Grumman” were formed by mergers. If you actually break apart Boeing’s merger history there were at least a half dozen WWII-era companies that slowly consolidated over half a century.

Part of this was because WWII subsidized an unsustainable and frankly absurd level of demand. For instance, Grumman almost exclusively built carrier-based fighters, and by the end of WWII they were producing planes so quickly that the Navy stopped doing periodic heavy maintenance of their aircraft in lieu of dumping them into the sea and replacing them with brand new planes. Obviously business for Grumman would never be quite that good ever again.