Somehow Christianity wasn't American enough, and that's why a few guys came up with the invisible golden tablets. It's the quintessential 19th century American religion, just like Scientology is the American religion of the 20th century.
To be fair, Mormonism does address a perceived problem with standard Christian doctrine that arose because of the discovery of the Americas. If Christ is sole path to salvation, how could a just god condemn the residents of the Americas for fifteen centuries to eternal damnation because it was impossible for them to receive his message. It does so by inventing a tale of Christ himself delivering his message to the ancient peoples of the Americas, and it addresses the problem more generally through its doctrine of baptism of the dead.
