I am not a biologist, so sorry to anybody for misinformation in this post.
If I understand correctly, dogs evolved the ability to show emotions through various sounds and tail-wagging in order to better communicate with their symbiotic partners, humans. Is it possible that recently, dog breeding has disassociated this with the communication of emotions due to the fact that humans like dogs which are more naturally happy? Considering that they have been tamed, and therefore their actions wouldn't be a good indicator, it seems plausible to me.
Please correct me on misinformation.