2 troy ounce silver coins contain 62.2 grams of pure silver and this is not a very common format. Series of coins of which the same coin type is issued in multiple weights often have a silver coin with a weight of 2 troy ounces.
For some issues it is decided to keep the same diameter as the more common 1 troy ounce silver coins. That way you get a silver coin that is twice as thick as the one troy ounce coin.
For special collectible coins, often with a limited edition, the 2 troy ounce format is very popular because it is a somewhat larger coin.