LOL, I spend a lot of time imagining WHY my dogs do things.
Andrea, I am lucky to not have had any of my own dogs have separation anxiety. Fosters and rescue, yes.
But all 3 of my basenji went through "i hate the crate/confinement". Cara still caterwauls if she sees me and is in her crate, but at least she has stopped biting the rails. I was afraid I would have to switch crate types, but she stopped. Had a friend with dog with wire that actually broke his jaw.
But back to known or guessed causes… The worse rescue I ever got for rehab was a Lhasa Apso, who literally lost bowel control if you got her near a crate. She had been locked in a crate and left in a basement, fed but lived in the crate, for we don't know how long. I spent 8 mos before I attempted to start getting her used to a crate again. And I placed her with someone who had a large cat room where she lived out her life with the cats and only was in a large kennel when she had to go to the vets. I agree knowing her history helped a lot.
BUT, I did "guess" one thing. She was afraid of the dark. As the sun went down she watched the windows and the fearful biting escalated. I am willing to bet that basement had little windows that went pitch black at night. But I don't know. And ultimately it didn't matter... we put her on prozac, kept night lights on, and eventually she stopped watching the windows and losing it at sunset.
I do know you couldn't pay me to rehab another one, lol. No muzzle with a dog that bites is not good. And they have razor blade teeth designed over centuries to rip yak meat. And yes, normally this dog would have been put down, but rescue wanted to give her their all because of the horrible abuse they took her from.