I think it's mainly caloric deficit manifesting itself in cravings. He must burn an incredible amount of calories just with his fidgeting and shaking. He only sleeps a few hours a night and will often just roam the house all night.

He's quite a few pounds down from his max healthy weight from 20 years ago, despite the fact he eats constantly. I think his body just thinks he's starving, so the natural response would be to crave calories and the easiest way to get those are sugary treats.

We do not dissuade him at all, since he could eat all day and not gain a pound. Additionally, he won't live much longer probably, so why deprive him of anything that will bring him happiness in the last stage of life which is otherwise so full of physical pain and mental frustration.