Winter and the Invisible Dog Doo

I still do not understand why dog owners think that their dog doo becomes invisible in the winter and therefore it does not need to be picked up. I walk the trails below the bike park as do many others and every day I can pick up at least 2 droppings left in the middle or just to the side of the trail.  I get that if your dog goes off in the bush, well off the trail, that's one thing but really - ON the trail?? If I have extra bags I will bag it hoping the owner will pick up next time around. There is something about dog doo that other dogs find very attractive and this can be a serious health risk to them.  Then when the spring comes and the invisible becomes visible we have a mine field of dog doo to step around and try to keep other dogs out of.  PLEASE be a responsible dog owner and take your doo with you.