Well, it is because that is the law. The various county taxes are used for a number of governmental services and one of those are the roads. So county taxes fund repairs and maintenance of county roads which nonresidents use as they commute to and from their place of business.
See the attached from Indiana:
https://www.in.gov/dor/files/dn01.pdf
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
