Have had the concert set lists discussion about other artists and I always end up with the same thoughts.  
The number of fans who are either lucky enough to make it to multiple shows is small.  
Those of us who regularly make use of resources like Archive.org is also relatively small. 
What may seem repetitious to some of us is fresh music for many others who may be going to a show for the first time . . or be completely new ears just  learning about the band.

Also, like it or not,  music has a business element and selling CDs is part of that.  The songs played at concerts hopefully encourages album sales and people will be looking for what they heard at their show.  Seems to make sense that the set list would reflect the CDs that are still available and can be easily found. 

As to TIS . . I love the album . . it was my first introduction to GPN.
NBTW was next and love those songs . .  same for Original Soul when got that one.  The earlier album is not available so don't know.
Now I do listen to the live sets from Archive more often . . especially ones of shows I attended.   To me that's just part of the evolution from discovery to "fan."  People I've introduced to GPN still start with TIS as a rule.  

What's next ? . . who knows . . but I don't expect artists as young as these talented musicians to forgo exploring possibilities and I'm curious and excited to see what's next.