Because they believe that smelling like another animal, even smallish predators, is better than smelling like a human. They seem to believe that deer cannot smell the carnivore/preservative/antiperspirant/toothpaste stench that is a human in the woods, and seem to believe that deer can't hear the difference between typical woodland creature sounds vs layers of waterproof clothing, heavy breathing, clearing of throats, and general fidgeting sounds the typical human perched in a tree stand makes.

Because hunters occasionally get a deer distracted and exhausted by the rut and the search for food post-freeze. And many, far too many, hunters bait deer with corn, molasses, vanilla, food plots, sorghum, sweet feed, maple syrup, etc.

The hunting product market is very lucrative, and as a conservationist who is pro-hunting for many reasons: hunters are gullible and believe all kinds of silly crap about animal behavior, which is reinforced when they occasionally kill an exhausted, hormone-drunk, or desperate animal.