Meav was partly, (if not fully) in charge of picking the songs, and I know with each show, all of the girls pick songs they might want in the show, so whats the big deal if they didnt want it in the show?! it was THEIR DECISION to not include it! Plus it wasnt performed in the original show at the Helix & that is what it looks like they wanted this show to be similar to. Yes, it is a great song, but they already had YRMU, The Butterfly, Si Do Mhaimeo I as staple songs in the show.
*edit* Oh and sorry I didnt realize you said tour, i wrote that before i saw that. Anyway..since you did say for the tour..I wouldnt rule out the possibility of them adding it as an encore during the U.S. tour and keeping it, since it IS a very popular CW song and has been since they started singing that song. I think they need more group songs, this show seemed to mainly focus on the girls solo songs & that bothered me a tiny bit. They will end up replacing 'Isle Of Innisfree' with something else & who knows if they will perform 'Tir Na Nog' on their tour in the States. Hopefully they do.
You raise some good points there. It's possible that they could add it for the US tour. How about this? If the song still isn't on the setlist when they tour the states, I'll create a petition asking them to add the song back in the setlist in 2017 after they finish their 2016 leg.