Grandpa is off the streets.
From his perspective, he gets free room and board, a roof over his head, fully covered medical care and even a burial benefit.
When you’re a senior criminal, life is a lot easier on the inside than out on the streets.
Generally, the other inmates don't prey on the old guys, and you are right, many of them have it better in prison than they do on the streets. I have seen it up close.
I think since he was in prison his whole life basically. I can see why he would miss it. I mean it is a mean place but I would imagine that they make genuine friendships and even get into a routine that they come to appreciate. I doubt the guy was going to hurt anybody at this point. He just wanted to get back to the life he knows.