In reference to coins from the 1970's. Especially "unpopular" 50c and $1 coins.
During that period, commercial banks would periodically sell these coins (in bulk and untouched still in the "mint bag" the bank received them in) direct to customers at face value.
The typical buyer profile was normally of the sort of type to hoard these bags. There are still more of these bags (and hence coins) NOT in the marketplace then are.