There are plenty of examples of unpopular rules successfully enforced, from school integration to the War On Drugs. The lack of mask/distancing enforcement is purely government cowardice and indifference. They could do it if they wanted to.
Publicly fire a few county bumpkin Sheriffs who refuse to enforce the mandates and you'd see an attitude change.
AFAIK most (all?) sheriffs can't be fired. They're elected county officials, so maybe they could be impeached but I really don't think they can be just outright fired like that.
Also, I would imagine many of the sheriffs that refuse to enforce mandates probably have considerable support from their constituents. Surely that would make their impeachment a significantly more difficult ordeal for whatever agency is responsible for the impeachment proceedings.
Publicly fire a few county bumpkin Sheriffs who refuse to enforce the mandates and you'd see an attitude change.