The rationale, supposedly, was that if government workers were allowed to be sued, they'd never get anything done.
That doesn't seem to have stopped Microsoft or Coca-Cola or Nike.
...what it would require, is government only hiring non-union, non-patronage, non "check the diversity box" people, who are
honest
and competent
and motivated
and conscientious
Obviously, the SWAMP can't have that! How could they reward their cronies while lording it over the rest of us (which is also unconstitutional)?