Cats may like to lick people's armpits for a variety of reasons. For example, cats have a natural habit of cleaning themselves, and they will often lick their fur to keep it tidy. This habit may extend to their interactions with humans, and licking human body parts, such as armpits, may be just a way for cats to demonstrate their affectionate and caring instincts.

Another example is that cats have a very keen sense of smell, and they use their sense of smell to perceive and understand their surrounding environment. Licking a human's armpit may be a cat exploring the human scent to better understand its owner.