Why? Because anthropomorphizing non-human animals is fun and useful. Yes, useful.
There's a reason humans love videos like this; after all, our tendency to project human qualities on animals stretches back well beyond the world's first ridiculous cat photos. Some researchers even think that, without anthropomorphism, neither pet-keeping nor animal domestication would ever have been possible. In other words: your tendency to d'aaaaw at this video may actually have pretty significant survival value.
It's also pretty adorable.