The main reason would be evolution. A nocturnal animal has developed over time to see better in the dark, camouflage into the darkness, and it most likely relies on scent more than sight. A diurnal animal would mainly rely on sight and smell almost equally, and have a pelt that can blend in with it's surroundings. The ranges also depend on the animal's habitat, whether its carnivorous, omnivorous, or herbivorous. Carnivores mainly rely on scent, omnivores seem to rely equally, and herbivores most likely rely on scent. Chances are, late humans did have stronger senses, but as we evolved past needing to scent predators and prey, we rely more on sight and only really use scent to recognise certain things. Humans aren't in as much danger as other animals anymore, for the most part.
