The entire tier system was created to ensure the state was able to collect a high amount of taxes on booze. When you allow it to be broken for "items not available here", you also open it up to a number of other problems.
You order XYZ super duper red blend from a California retailer because it is not available in KY. The same california retailer also sells captain morgan rum for less than "wholesale" cost here in KY. You start ordering Capt Morgan by the case along with your XYZ wine because it is cheaper (even with shipping). The state of KY does not see any tax money from the sale of alcohol in this case.
The consumer benefits in this case and the state doesn't miss out on much.. Now imagine retailer in KY also sees this loophole and is buying Capt Morgan for significantly cheaper from California not by the case but by the pallet. Multiply this times 100's of retailers and customers.
and what do you have there? Just free enterprise, a system that promotes the purchase and delivery of goods at the lowest cost, laws forbid that should happen!
Simple rule of taxation: as long as volume is low, tax authorities look the other way. As soon as volumes become significant they want their cut.
Similar situation happened in the early days of internet shopping, practically everything came over the border without tax, as soon as the majority of people began to use the system government stepped in to make sure courier companies collect tax. The courier companies complied because they also add their own tax in the form of brokerage fees for collecting tax on behalf of the gov.