"They were not required to leave the foreign service but chose to retire or resign for personal reasons, the department said."

That statement says it all. I spent 20+ years working for the U.S. federal government and can guarantee they wouldn't walk away from a permanent slot because a new boss was elected. Re-entering the work pool with a good possibility a Burger King manager position is in their future is career killing  move. Trump may be a partial reason or final push but they were  ready to retire and collect their pensions. Those not eligible for retirement moved on to other government positions.