Why do dogs live so short a time?

I couldn't resist posting this lovely piece for dog lovers everywhere:

Being a veterinarian, I had been called to examine a ten-year-old Irish
Wolfhound named Belker. The dog's owners, Ron, his wife Lisa, and their
little boy Shane, were all very attached to Belker, and they
were hoping for a miracle.
I examined Belker and found he was dying of cancer. I told the family we
couldn't do anything for Belker, and offered to perform the euthanasia
procedure for the old dog in their home.
As we made arrangements, Ron and Lisa told me they thought it would be
good for six-year-old Shane to observe the procedure. They felt as though
Shane might learn something from the experience.
The next day, I felt the familiar catch in my throat as Belker's family
surrounded him.
Shane seemed so calm, petting the old dog for the last time, that I
wondered if he understood what was going on. Within a few minutes, Belker
slipped peacefully away.
The little boy seemed to accept Belker's transition without any difficulty
or confusion. We sat together for a while after Belker's Death, wondering
aloud about the sad fact that animal lives are Shorter than human
lives. Shane, who had been listening quietly, piped up, 'I know why.'
Startled, we all turned to him. What came out of his mouth next stunned
me. I'd never heard a more comforting explanation.
He said, 'People are born so that they can learn how to live a good Life
-- like loving everybody all the time and being nice, right?' The
Six-year-old continued, 'Well, dogs already know how to do that, so they
don't have to stay as long.'
Live simply.
Love generously.
Care deeply.
Speak kindly.
Remember, if a dog was the teacher you would learn things like:
When loved ones come home, always run to greet them.
Never pass up the opportunity to go for a joyride.
Allow the experience of fresh air and the wind in your face to be pure ecstasy.
Take naps.
Stretch before rising.
Run, romp, and play daily.
Thrive on attention and let people touch you.
Avoid biting when a simple growl will do.
On warm days, stop to lie on your back on the grass.
On hot days, drink lots of water and lie under a shady tree.
When you're happy, dance around and wag your entire body.
Delight in the simple joy of a long walk.
Be loyal.
Never pretend to be something you're not.
If what you want lies buried, dig until you find it.
When someone is having a bad day, be silent, sit close by, and nuzzle them
gently.

And oh, don't I wish I was the kind of person my dog (above) thinks I am!