It is known that dogs can "cover with kisses" all parts of the body accessible to them, but the hands receive the most attention.
This is easy to explain if you understand the nature of the animal's behavior.
Most often, experts indicate this reason as the dominant one: with such a gesture, the dog simply wants to show that the person is important and interesting to him.
But "washing" your hands becomes a simple way to show concern.
This gesture seems strange to us, but for dogs it is normal or even habitual. Often animals show their respect to the leader of the pack when they start licking him.
So the dog does exactly the same.
This gesture is well known and familiar to the dog, so it is not surprising that the animal practices it.
The dog tries to please its owners and clearly does not put a negative meaning into its behavior.