Coins don’t cost what they are worth to make.
Other than that, coins are cheaper than bills on the long run, because they last longer. It would be cheaper for the US government to stop making $1 bills and have people use the $1 coins, but I guess old habits die hard.
(Or at least they used to; when I visited back recently many supermarkets had free trolleys! Can you imagine my shock?)
Is this not a thing in other countries? How do they get people to return their trolleys to the bays?
And did Britain have this before the invasion of Aldi and Lidl?
There is no external force compelling US shoppers to do so. This has led to the (in)famous "shopping cart theory" [0], first posited like this:
The shopping cart is the ultimate litmus test as to whether a person is capable of self-governing.
To return the shopping cart is an easy, convenient task and one which we all recognize as the correct, appropriate thing to do. To return the shopping cart is objectively right. There are no situations other than dire emergencies in which a person is not able to return their cart. Simultaneously, it is not illegal to abandon your shopping cart. Therefore the shopping cart presents itself as the apex example of whether a person will do what is right without being forced to do it. No one will punish you for not returning the shopping cart, no one will fine you or kill you for not returning the shopping cart, you gain nothing by returning the shopping cart. You must return the shopping cart out of the goodness of your own heart. You must return the shopping cart because it is the right thing to do. Because it is correct.
A person who is unable to do this is no better than an animal, an absolute savage who can only be made to do what is right by threatening them with the law and the force that stands behind it.
The shopping cart is what determines whether a person is a good or bad member of society.
https://taitc.buzzsprout.com/2186249/episodes/17383823-the-p...
It's a different story if the material value of the metal in the coin exceeds its face value - at that point it makes sense to go to a bank, change money into pennies, then scrap them and sell the copper. That would be bad.
But the reason pennies are a bad deal isn't because of their manufacturing cost, it's because their handling costs exceed the value of incorporating them in a transaction. Should a store go to the trouble of keeping pennies available, counting them, storing them, transferring them to the bank? Or should they round up change to the nearest five cents and take a 4c hit on each transaction where you'd have been able to use pennies? If your average transaction value is over a hundred dollars or so, like most supermarkets, and you only handle cash on one sale in 50 say, if handling pennies in your cash-management operation takes more than a few thousandths of one percent of your budget, it's costing you too much.
Well, that is highly illegal and not very profitable vs the amount of risk. You'd be better off doing almost any other crime.