Because if you want to eat an animal you have to properly remove the bits of it that will make you sick and spoil the meat.

We do it to pigs and chickens and cows too. Its a very early step in the slaughtering and butchering process - usually the first step after the animal has been killed.

Because you're poor and need to hunt squirrels to get protein into your diet?

Or because you have a history of being in that position and feel like it is important to pass the knowledge on?

That isn't what was written on the letter, that was the commenter's own writing.