You won't find a much bigger fan of the AB songs than me, but let's be real. People do not know Ultraviolet outside of the die-hards. And it has not been played live since ZooTV.
When the band tours, they are touring the new album. As a result, they are likely to play many or most of the songs from the album in an effort to boost sales. Most bands do this. So for starters, consider they have to play a handful from the new album - let's say 6 or 7 songs.
Then, they have a list of at least 20-30 solid "hits" that they can rotate through. They have to play these to appease the masses, and remember that the majority of people at a show are casual fans with an appreciation and solid knowledge of probably 10 U2 songs at best. U2 have a large enough catalog now that they are literally going to have to pick through the "hits" and be selective.
So 6 or so from the new album, 20 or so hits - you've already filled up more than enough for a single setlist.
Now consider that from time to time they rotate through a few of the songs on the new album, adding some and dropping others as they learn what work and what doesn't in a live setting. At the same time they are also rotating through their catalog of hits, changing that up from time to time.
The end result is that the rare, obscure gems like Ultraviolet stand little or no chance of ever being played live. If anything, we're more likely to hear a moderate or lesser-known "hit" (Wild Horses, Gone, etc.) than a song that was never even released.
Just trying to keep it realistic...