Here’s a timeline chart
https://usafacts.org/articles/how-many-people-work-for-the-federal-government/
Aside from immediately after FDR the federal government has been fairly steady at 3 million personnel. FDR tripled federal employees and its stuck like glue since.
What’s also interesting is the amount of DoD civilian employees has not changed since at least 1980 at around 800k employees, at the same time military personnel has dropped 39% in that same time period.
https://usafacts.org/articles/how-many-people-are-in-the-us-military-a-demographic-overview/
I can’t imagine anything other than set government bloat that has made a consistent need for 3 million personnel.
It's a lot easier to pretend to be busy when you have to and use the scanner all the time, looking important with a stack of papers walking around.