Why are there 2 GTX 970's from Gigabyte on Amazon?

Solution
Because most of the card manufacturers have different models of each series. Some card models in the same series have more memory, some are overclocked from the factory, there are different cooler configurations and other models may or may not come with a backplate.

Between those two the G1 gaming is the higher performance model and is generally speaking the most commonly recommended of all the 970 cards. Manufacturer preference is sometimes a personal choice but of all the cards out there that one has the best reviews.
Because most of the card manufacturers have different models of each series. Some card models in the same series have more memory, some are overclocked from the factory, there are different cooler configurations and other models may or may not come with a backplate.

Between those two the G1 gaming is the higher performance model and is generally speaking the most commonly recommended of all the 970 cards. Manufacturer preference is sometimes a personal choice but of all the cards out there that one has the best reviews.
 
Solution