Because it's amazing.
This is my favourite ad right now. It makes me feel like I should become a guide dog trainer! Seems like a pretty sweet job, I mean you get paid to train this adorable puppy and even though you have to give it back, you get a new one that's even cuter!
On a serious note I sometimes get mildly teary when I see this ad.
But that may be just because I don't have a labrador puppy.