If that were the case (a President can overturn a previous President's EO), then why is Kennedy's EO to allow Unions in Public Sector employment NOT over-turned? What about all the Regulatory Agencies that have been created?
Picking up a pattern here?
For purely political reasons. If an eo allowed unionization of fed workers then a similar one could disallow it.
Is it not true what an eo creates another eo can uncreate?