The Sheriff is the only law enforcement officer in the US that the people vote for. All others are appointed.
This brings the most powerful enforcer of the law in the US very close to the citizens and voters. They know this person and can personally remove them from office in small elections.
State attorney generals are voted on by state elections, and it's unlikely many people know or can meet an attorney general.
The Sheriff is a county election, and is likely to be known (or even well known) in the community even before being elected.
I have been told by a sheriff deputy that the sheriff is the highest authority in the county, above all other authorities, that even the Presidents have to ask permission to enter their county. I am guessing this would include attorney generals as well.
This brings the most powerful enforcer of the law in the US very close to the citizens and voters. They know this person and can personally remove them from office in small elections.