U.S. travelers are certainly aware of the challenges of dealing with visa applications to visit certain countries, and how much simpler it is to visit somewhere that either doesn’t require a visa for U.S. citizens or allows for visa on arrival.
The U.S. won’t allow foreigners without approved visa or ESTA to board aircraft headed for the U.S. That raises the transaction costs of coming here, which makes doing business with the U.S., spending tourism dollars, and supporting U.S. industry more difficult for little security benefit in exchange.