That's not accurate. If you fail to pay the county, their lien on your property allows them to seize the property, sell it at public auction, recover their debt plus expenses from the proceeds, and then give you whatever is left of the proceeds. They do not have to wait for you to sell the property before collecting. The details on how long you have to pay and the exact procedures vary from state to state (maybe county to county), but that is the fundamental law.
It's no different with vehicles like cars and aircraft. If someone holds a lien on your vehicle, and you do not pay the debt within the legally defined time, they can obtain judgment to have your vehicle seized and sold to make good the debt. That's exactly what's happening on that Aircraft Repo TV show. The big difference between this subject and that show is that the aircraft in that show were in the possession of the debtor, not the creditor, so they had to repossess the aircraft first. Were the aircraft still in the creditor's possession, there would be no work for the Repo boys.
Anyone who doubts this need only take their car to the shop, have work performed, and then refuse to pay the bill. I guarantee you will not legally drive away in that car, and calling the sheriff won't help you.