There will be exemptions for legitimate uses of nitrous oxide, for example in medical or catering industries. The gas is commonly used as a painkiller and for producing whipped cream in cooking.
I didn’t say it was simple, but it’s straightforward and very far from unfeasible.
It sure is a thing that can be done, it’s just a lot of effort and possibly cost for what it might achieve
But there are tons of costs with criminalisation, too. The cost of police time, the cost of court time, the cost of prison, the loss of production from otherwise good citizens being made into criminals. Which is the better use of public resources? Which would be more effective at actually preventing cannisters from being left around everywhere?
Edit: If anything, making it illegal could lead to more litter. People aren’t going to hang on to their empties if they could be used as evidence of a crime.
It seems strange to me to even consider the two as ways of combating litter