Because the results you get from positive interaction are much better than those you get from negative interaction. While there will be cases of negative interaction, such as giving meds or grooming, and negative training, "stop right now!", these should be far outweighed by the positive.
Dog-to-dog communication is far from all negative.
Some dogs do give others a treat of sorts to encourage play/interaction with other dogs. For example, last week at the dog park a poodle brought over her tennis ball and dropped it in front of our dog trying to get her to play. Our pup, who's only 6 months old and still a bit unsure around other dogs, joined play after this friendly gesture.
Dogs don't have a pack hierarchy as it's traditionally thought of. They're social animals that will form loose associations based on their current needs and situation. This isn't the stable pack/family relationship found in wild wolves.
Dogs also also adept at forming social relationships with other species, including humans and other pets (some more than others). This isn't a pack but a social cooperative relationship.
Dominance is often used as an excuse for abusive or potentially abusive and often dangerous and ineffective training techniques. That's why it's viewed not being good by many. Dominance is also incorrectly used by some as a blanket cause for many dog problems which isn't the case.
Dogs are naturally bilingual. Not only do they understand dog-to-dog communication but human-to-dog communication. So, communicating with humans has, over many centuries of breeding, become part of the natural dog. It actually confuses them when a human tries to speak dog because it doesn't seem natural to them.