I've been to many folk concerts where I couldn't understand a word. My theory is that they are amplified so much that the syllables hit the walls, echo off and mix with the new syllables coming out.

The singer may think his diction is fine. The sound man has heard all the songs, knows the words, and thinks they are fine. Most audience members think that if it's loud enough, it's fine.

I'm the odd one out.   

It's not just folkies. To please a friend, I attended Phantom of the Opera, and the only lyrics I understood in the entire show were 'tum ty tum ty tum ty OF THE NIGHT.' But everybody else was happy because they owned the album and had learned the lyrics at home, so they could follow them.