This is a sign that cats are distinguishing each other through smell. This habit is the same as that of dogs. Cats mainly understand the world through smell. This is why cats like to rub their butts in various places in the house. The reason why they go is that they leave the smell behind for easy identification next time.

Tip:

When the cat recognizes that you like you, it will leave a scent on your legs that only it can distinguish, so that it can recognize you next time.