That is not the only cause for the variety of US Gold Coin. Once upon a time America was nothing more than 13 colonies fighting for independence. It was during that time period when nearly any minted gold coin could be used for commerce. In circulation with the various European gold coins in use, there were actually gold coins that were minted for the wealthy using their own gold for the currency. That changed with the Coinage Act of 1792; it was that law that helped established the United States Mint and put them in charge of regulating the variety of coins out there.
But wait, there is more. Since the creation of the federal authority on gold coin and currency, there have been dozens of people in charge. While some wanted to make their mark on the world by designing their own gold coins, others such as Mint Director, Robert W. Woolley, believed it was his legal responsibility to change the design of US Gold Coins that had existed for more than 25 years.
Here is another for reason for so many US Gold coin varieties. Gold coins were no longer to be used as legal tender thanks to the 1933's Executive Order 6102 that made it illegal to hoard gold as a response to the Great Depression. That made the previous gold coins no longer of use, making US Gold Coins such as the Saint-Gaudens double eagle and a three-dollar piece a part of our nation’s history and another variety of US Gold Coin.
Now, it is a marketing plan that fuels the recent crop of US Gold Coin options. While a gold investor may not necessarily care about the variety of US Gold Coin they have (as they buy gold thinking about purity and weight) coin collectors get excited every time a new US Gold Coin is struck. Numristics collect coins not just for the gold content, but for beauty, history and rarity; each new US Gold Coin may be of interest to them.