Many believes ghost and spirit are not related to human, they exist separate it. I think the same apply for when these people view animals as separate from human. Once a human die one doesn't become spirit, animals, or some other existence, not related with 'me'. As for after-life when death comes, people probably has the idea that it means non-existence, you couldn't do anything about it. Even if there is after-life so to speak it off, it could be another form of existence, non-related with spirit, or animals whatsoever.
The idea of next life is not mainstream. It is not in the mass consciousness. It is not part of parcel, not counted, in our every day living. Why? Perhaps most of us are brought up to think only of study and work, concern of yourselves. And the education system doesn't talk about next life, being spiritual, what to do investing in your future lives.