No, I think its the fact that it is very mellow without any signature U2 crescendo. Their shows have always catered to the masses, and with each album, every song has to fight even harder to get played. Will it get played--yes. But I think the rsponse in a stadium will be underwhelming, and they will realize this. I am sorry, this song does not have the classic U2-ness that a crowd of 60,000+ will take to in a stadium setting.
They are not a band that shuffles the setlist--As a Horizon member I hope I am wrong (I'd love to hear it), but U2's setlists have always been on the "safe" side. I really do like the song, but I just do not see it breaking through--Cedars also has that beautiful subtle shimmer, and I can guarantee that will not get played on a regular basis (if at all).