Are we overlooking the crime associated with corporate management, the featherbedding, and how non-union company employees abjectly failed to thrive in the -- what's a "post-post-WWII era" anyway?
Post-WWII is a strong period for unionized employees and companies, with much of the competition suppressed by war time damage, and the playing field less tilted toward unions by the Taft-Hartley Labor Act of 1947. Post-post is after that, when many if not most unionized US industries declined, e.g. steel and auto.