"so many S.S songs are personal enough to be 'private' songs "

There is no denying that there are "personal" songs among singer-songwriters, but the better artists are creating songs that do fit the universal theme.   Love is probably the most personal, yet universal theme there is. Barbara Allen is an artifact of the style of its time, and contemporary singer-songwriters are writing on the same theme in similar terms that can be touched by all.

No one likes to sit through someones therapy session, and writers get that.   

It is too easy to generalize about singer-songwriters, I admit to falling trap to it too. I used to call them singer-songwhiners. Then I started to pay attention. I was wrong to use such stereotypes. When you really start to listen you will find a body of work that can be considered folk of it's time - depending on how you interpret the definition.