Why is crate training a struggle?

One of the first things many people who have dogs with separation anxiety notice is that crate training is hard.

Like really hard.

And the crying, protesting, is different than anything you've ever seen before.

Doesn't matter what you try or what information you find that's supposed to help, none of it does, and the crying just gets worse. Why is this? First, it's not because you are doing something wrong. It's because dog's who struggle with separation anxiety struggle with confinement anxiety or being confined.