It's a safe and reliable way to dispose of a corpse that might be diseased, will smell bad as it decomposes, and would certainly attract scavengers if left lying around. The same goes for cremation, it really just depends on local custom.

Why let all that meat go to waste?

If you think about it it is not strange at all, it is maybe one of the very early things that differentiated us from animals. We have a concept of death and time, future and loss. We mourn our dead. And I strongly believe that all the rituals that we have established are not meant for the dead but in fact serve the living. It is a way to cope with the loss of a person. And with the ever same ways - casket, flowers, music, burying - we give the mourning something to do and get distracted so that they don't lose themselves in the sadness. It feels "right" because it feels familiar, everyone does it this way. You don't have to reinvent the wheel every time someone dies. How to cope, and how to get rid of the body? Well, there is a societal playbook for that.

There was a dude here on lemmy who actually specialized in American death rites. I think he stopped using lemmy though because of too much negativity, I think people commenting how stupid it is that we don't just trash our dead on a post was his tipping point. Which is a freaking shame because it sounds like he knew some really fascinating things.

Leaving a carcass in the wild would attract scavengers and spread disease, which is prevented by inhumation. Cremation is also an option but requires a large amount of fuel. In early and prehistoric cultures, inhumation was the easy option.

Edit: to add to this, I read something on how the first "burials" were just piling rocks on top of the dead body, primarily to ward off scavengers. So, aside from honoring the dead, burial and cremation have a practical purpose as well.