But a lot of the songs they sang weren't real folk songs. The correct name would probably be more like neo-folk songs. If I wrote a song today protesting the Obama admin, it wouldn't be a folk song just because I played it on my acoustic guitar. It would just be a song.
Most good folk songs have stood the test of time. While many of the very old folk songs certainly were political in origin, most weren't. They were the popular tunes of their time. Like today, most were love songs. Many were about simply having a good time. Some told the news of the day. And there were a number that were political and unpopular with the powerful. But the communist folk music movement tried to inject their leftism into every song they sang.
And a lot of the greatest folk music is the non-verbal, dance music. Think Irish and Scottish jigs, reel, hornpipes and the like. It took me until I was almost thirty (I'm sixtyfour) to discover this whole other world of folk music that wasn't about hating rich, capitalist warmongers and making a new (commie) world for the masses.
Murder ballads.