There will always be people who do not pick up after their pets regardless of weather. Then there are those who for various reasons,  don't pick up after their pets only in inclement weather. Perhaps they don't want to follow their dog into the snow, or they have to remove their gloves and they don't want to. Perhaps some people think the cold weather will destroy any parasites so they don't worry about it.
On the contrary, some parasites can survive the cold. Giardia, for example, can survive for approximately 7 weeks.

Think about that. Your dog can be sniffing, licking, eating infected feces in the winter. I find most people are aware of this in the Spring and Summer but not so much in the Winter months.

Take a moment to think about Spring thaw. Think of all the feces melting as the temperature warm up. Not a pleasant thought, nor smell.

For those of you reading this who don't pick up poop in cold weather (or not at all), think of Spring and what your dog will be walking in, sniffing and possibly ingesting as well as bringing into your home.