Eckhart Tolle explains why dogs live in constant joy: they have no ego, so they simply exist without the mental noise that blocks humans from feeling the same ease. We're drawn to them because they show us what's possible.
Chapters
The dog is a lovely being that's much more at ease, cats too, much more at ease with life than humans, much more able to experience joy than a human being. This is why humans love their dogs, because the dogs can show them the possibility of being in that state of joy for seemingly almost no reason whatsoever. You just look at them and they're entertained. Tail starts wagging. It's the joy of life. Why are they so joyful? Do we just look at them? Because they don't have an ego. They just immediately, they sense the joy of being, the joy of being.