Production of United States Mint American Eagle Silver Uncirculated Coins continues to be temporarily suspended because of unprecedented demand for American Eagle Silver Bullion Coins. Until recently, all available silver bullion blanks were being allocated to the American Eagle Silver Bullion Coin Program, as the United States Mint is required by Public Law 99-61 to produce these coins “in quantities sufficient to meet public demand . . . .”
Although the demand for precious metal coins remains high, the increase in supply of planchets—coupled with a lower demand for bullion orders in August and September—allowed the United States Mint to meet public demand and shift some capacity to produce numismatic versions of the American Eagle One Ounce Silver Proof Coin.
Read more here