A sad one

So, two years ago my grandfather had a stroke and it's rendered him unable to take care of himself. I love him to death, but I can tell he hates living this way. He used to be this big, 85 year old guy who was jacked. Always taking care of his wife and family when the need arose. He was cheerful and happy. Now he can't walk or even eat properly by himself. Hell, he can't even talk without it sounding like a muffled, foreign language.

I love him to death. I help take care of him and it inspired me to start making my own foods and dishes. I don't mind any of that, but I just hate this unfathomable sadness I see in his eyes every time I see him now. He's slender and I can tell he feels like people look down on him now. I just don't want him to feel that way anymore. I try to hang out and do my best to make him feel better, even when he went to PT to get his ability to walk back, I was there to help out and try to encourage him. He gave up on that after six or so months. He'd go, but he wouldn't try anymore when he got home.

My grandmother isn't the kind of person to listen to you unless you take charge either. He can't do that anymore now, so she doesn't really listen to him. I hate knowing how he feels. He'd never let anyone know how he felt. He's like a 30's/40's OG who changed how he behaved to take care of his family and provide. Talking about how he feels isn't even something that'd cross his mind. I've tried, but he just doesn't want to. I know how he thinks. It's almost insulting, in his mind, to think he'd even feel down about something like this.

TL;DR:
Grandpa had a stroke a while ago and gave up on trying to fix his body shortly after. He's super depressed and there's nothing I can do for him. I hate knowing he feels this way and feels useless. I don't know what else I can do for him.