Men are far less polite. Puppy love doesn't wear off so quickly with a dog. You can be prosecuted for neglecting a dog. Dogs can find their way back home - even after a really heavy night out. Dogs can be trained not to lie on the bed.
Men always lie in bed.
A dog can moult without becoming obsessed about premature baldness. Elizabeth Hurley has a faithful dog whom she loves dearly. If a dog says sausages, that's clever. If a man says sausages, that's just greedy. A dog will fetch the morning paper for you.