What is wrong with people who get sad about their dog or cat dying?

My dad died a year ago, my granddad died 6 years ago, my stepdad died 2 and a half years ago, and my friend that I knew since I was 3 years old, died 4 years ago. They all died unexpectedly, I have never felt the slightest bit sad about any of their deaths. So to be sad over an animal just seems ridiculous to me.