Dogs lick and sniff their owners for the same reason they lick and sniff each other. It’s their way of reinforcing pack bonds and reassuring both you and them that you’re a part of each other’s lives. Their memories aren’t that long so constant communication and socialization are important. It’s a matter of survival. They’ve evolved alongside us for about 40k years and many of their behaviors came about due to their companionship with us. It’s vital to them that they remind us they’re important to us.