There’s plenty of air pollution in the countryside too from eg muck spreading or turning industrial compost heaps. It’s not really clear how bad they are
At least in the city you have constraints on how much traffic can fit and alternatives to driving.
I think if you go to just about any moderately popular walking spot in the uk with steep stony parts, you will see just about every rocky step is covered in the scratch marks from the feet of the poles. One wonders if they are really effective if they can’t get a good grip on the more difficult terrain people presumably get them for help with.