system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why did big name musicians like Johnny Cash and B.B. King play concerts in prisons so frequently?
gpt
It was a phenomenon of the 1960s.

Prisoners didn't have much in the way of rights nor did anyone much care how they were treated or housed until the 20th century.  Until then prisons were squalid, damp, cramped, pest-ridden hellholes.  Prison was a punishment.  But in the 20th century people started to realize that if you put a human into a place like that, kept them there for some number of years, then let them out, they were likely to be more dangerous to society after they were released than they were when they went in.

So (at least in North America and parts of Europe) people began to think of prisons as a place for rehabilitation.  Prison, in and of itself, was not supposed to be punishment.  The time served was.  Prisons were supposed to be places where broken people could get "fixed" and returned to society as better than when they went in.

Still, the legacy of the old-style prison as punishment lasted, in large measure because the prisons themselves lasted.  Its hard to justify tax dollars to tear down a perfectly good jail and build a new, nicer facility for murderers.

By the 1960s societial views had begun to change and a growing sympathy was felt for prisoners.  The idea that they should still have some rights, and be given some humane experiences like libraries, concerts, religious services, etc. gained strength.

Cash, and others like him who went into the prisons in those years were at the vanguard of that movement, raising awareness with the public about what conditions were like and making people feel more should be done to improve them.  That's why, for example in Cash's Folsom Prison recording they included the audio where he talks about the water and how disgusting it is - that's not meant to just be a funny bit, it's meant to make listeners who knew nothing about prison have an emotional connection with those men.  Surely, you would think, at least the *water* should be clean?

Cash had always been fascinated by the struggles of the lower classes.  Farmers on land washed away by floods, men working on railroads far from home, prisoners, indigenous peoples, etc.  He made a lot of money singing songs about their lives and received a lot of mail from people like those he sang about.  His religious beliefs were also centered on salvation and redemption and who needs that more than someone in prison?  He was a natural fit for this movement.

Over the years those kinds of concerts have continued but now it is much more about the prisoners and less about society.  People do them out of a sense of sympathy for the imprisoned rather than as a way to wake up the voters about conditions "inside".