Not entirely true. A governor can suspend a sheriff who is suspected of illegal or improper activity and appoint a temporary replacement until the allegations have been investigated.
When I lived in FL a governor did suspend a sheriff who was ultimately indicted and prosecuted. I don't remember which governor or which sheriff, but I do remember that it happened. Probably sometime in the 1980s, but I'm not at all sure.
Probably Ed Stack from Broward Co.