Mammals lack mucus glands in their skin for several reasons. One reason is that they have fur, which provides a barrier against moisture and keeps the skin dry. Another reason is that mammals have sweat glands, which help to keep the skin cool and prevent it from getting too wet. Finally, mammals have sebaceous glands, which produce oil that helps to keep the skin soft and supple.
Mucus glands are found in other animals, such as reptiles and amphibians, but they are not common in mammals. This is because mammals have evolved different mechanisms for keeping their skin moist and protected from the environment.
