One of the problems besetting the folk revival(s) is the pseudo-romanticism of a Rousseauian "Noble Savage". It shouldn't be any surprise to any student of folk music or folklore that far from being "noble" many songs contain lyrics that are as violent as any rap song by "gangsta's" today. Just because it's folk, doesn't make it edifying.
It's more apt for poorer people from agrarian cultures or those in a manufacturing community to sing of their problems then it is for the comfortable and well-heeled but many of the songs we call folksongs were composed or written by those not from this economic class.
In the Thirties and Forties folk music was used by the Left to outline "class struggles" although there was a counter-current in the American rural South that would have been deemed politically incorrect by well-meaning Lefties. Many of these latter folk songs survive.
The "obsession" is something aside from the statistical aspect of folk music which as we understand it does come mostly from those who were denied the advantages of a middle-class education and were at the mercy of merciless politicians and business people who exploited them culturally and economically. This doesn't mean that every folk singer was poor or exploited. Some who have come from humble beginnings have made their way into the annals of scholarship such as Jean Ritchie. Even the legendary Woody Guthrie had middle-class roots at one time in Oklahoma (named after Woodrow Wilson). Pete Seeger was a Harvard drop-out with a middle-class beginning in academic circles.
But the music itself is recognizable not as an emblem of middle or upper class values but as an expression of working class people in its lyric content and reductionist music. It also has the power to get people to sing along from all economic classes because it contains this expression of social class.
The folkies that are obsessed are like any other group of cultists or faddists.