Back in the mid-2000s, I worked for a major university large animal hospital. During that time, I cared for many neuro and “down” horses.
When a horse is ataxic to the point they can not stand under their own power, the prognosis is bleak. They can’t eat, they can’t hydrate themselves, their guts can’t function correctly, and worst of all, their bodies just aren’t meant to support 1000lb+ laying on its side for any extended amount of time. Everything ultimately stops working. The larger the animal, the more difficult it is for them to recover.
There is no reason to speculate anything nefarious was happening in short of a very sick horse.
The four day time period is not suspicious at all, as these things are often touch and go with positive responses to treatment in a race against developing complications.
Arrogate was undoubtedly receiving very labor intensive, around the clock supportive care with the hopes of recovery. Downed horses need to be turned onto their other side every few hours, which is one of the most difficult and dangerous things you will ever do with an animal. They may have been using a sling, but slinging a horse is an arduous process with limited applications- the movies make it seem so easy when the reality of slinging a sick or injured horse is quite complicated. For a horse who has lost all coordination, a sling won’t help except to possibly aid in the turning process. A horse has to be able to safely control their body parts to use a sling for an extended period of time.
It’s always unbearably sad when we lose these great athletes so young. My heart goes out to his connections.