I think the main issue is that U2 want to be the biggest band in the world (and are) and you don't get to that position by playing to a hardcore minority (however vocal that minority is).
I went to see them with 3 friends at Manchester 2 this year, one of whom is a big fan, the other two are casual fans. I would have liked to hear "Tomorrow" "MOFO" "Bass Trap" et al, but it would confuse the concert for the others not so familiar with that, which would in turn give a negative vibe.
I think ZOO Station is a great song, but I felt it tripped the setlist up a bit since a lot of people are unfamiliar with it.
I went to only two concerts this year (my first two) simply because I couldn't afford to go to more. A lot of people will only go to one, and they pay the same money as the hardcore types so they deserve to have a show they can get into, which means "Streets" "Beautiful Day" "Vertigo" "Pride" etc.
The basic point is: if you want to be the biggest band in the word and put on arguably the biggest tour ever seen, you aren't playing for the hardcore minority.