Cats may climb on people because they find it a comfortable place to rest. Cats may also sometimes want attention from their owners or want to express their caress. In addition, the cat may also want to take a look at the surrounding scenery, or want to observe the surrounding situation from a high place. Sometimes, cats may climb up because they think there is some good smell on people's bodies. It's also possible that they climbed up to chase something on someone's body.
In short, there are many reasons why cats climb on people. They may be out of warmth, attention, and good smell. Or other reasons. If you don't want your cat to climb on you, you can try to provide it with a separate place to rest, or provide it with some game toys to help it deal with its excitement.
