But, while coins are durable, the Mint has been making billions of pennies every year since the 1950s, and yet retailers have trouble sourcing enough pennies to make change. They do tend not to be recirculated, even if they're not disposable.

You can buy pennies or nickels in bulk, melt them down, and turn a tidy profit. That's literally a "money printing glitch"

Every penny or nickel that gets lost in the gutter, stored in a coin collection, used as a washer or shim, turned into jewelery, or sets around in jars unused, represents a financial loss to the Treasury.

It's called seigniorage and melt value. Also see Gresham's law (hoarding).