Why???

In the eyes of a dog, petting is licking. Dogs see human hands as if they were some sort of extra heads, well not quite, but you get the idea.

I licked my Husky back once and she was CONFUSED. She didn’t know what to do.

Because that would be bestiality

Please don't lick your dog

It's all just a form of affection/grooming/scent marking to them. Plus, iirc dogs and cats supposedly like that our skin tastes salty