If they wanted to reduce the amount of useless receipts to curb consumption, just put a tax on receipt paper at the point of manufacturing. Increase the price there, and the market will automatically use less of it. And the tax can then be used to mitigate the effects of what receipt paper is produced.

It's far, far easier to regulate a dozen (or fewer) paper companies than it is to regulate millions of retail points of sale. The same goes for plastic: If the price of a gram of plastic included mitigating the effects of producing it, the price would be higher and therefore there would be less of it. And that which exists will be less likely to be wasted.

Externalities are one place where free market theory breaks down and needs regulation. Taxing at the source puts a price on this externality as soon as it enters the market, so the market can adapt to it.