Someone down our trail with a little dog just gathers some leaves and sticks to cover it. Now that it's winter they push snow over it. How much harder would it be to bag it or flick it into the brush beside the trail?
I do know how some piles get left though, those ones that proliferate in spring when the snow has melted away. Their dog goes off the trail, usually just a narrow footpath in the snow, to poop. If they step off to pick it up they sink much further into the deep snow than the dog did, so they leave it. Come spring we all find it's ON the wider bare ground trail. I stepped off our trail last week and went up over my knees into snow. The crust would hold my dog but not me.