The problem with average life expectancy is that most dogs don't die of natural causes, they get put down. We would have a shorter average life span if we allowed people assisted suicide for those with terminal conditions, especially ones that drag on for years or decades. Think ALS, Alzheimers and Parkinson's, they can last twenty or thirty years. Often long past when a person would want to die for the benefit of themselves but also everyone around them.

We make that choice for our dogs. My in-laws put their dog down, he likely could have got another year but he was suffering and you don't torture things you love with forcing them to stay alive.