In all fairness, one of the challenges with Europe is arena size; there just aren't that many arenas in Europe that are 16,000+
Somebody above mentioned Glasgow; that arena holds about 12,000; that's just too small for the band at this point.
I was surprised that they didn't play more JT stadium shows, especially with the demand, but I do understand why they are limited as to the arenas they can play with this set up
There are 25 arenas in Europe with a capacity over 16000.
https://en.wikipedia.org/wiki/List_of_indoor_arenas_in_Europe
Also like mentioned the US has tons of big Ice hockey arenas that are modern, even in smaller cities. And they have huge NFL and College stadiums in every state basically. Europe usually have stadiums that are older in age as well even if they are big, many of them are from the 50' - 70's. We have very few Wembley caliber stadiums in Europe where they got alot of new NFL stadiums in the billion dollar category.
13 of the 16000+ stadia in Europe were opened since 2000 ,most of the rest are pretty modern too so I dont think that argument is correct nowadays.
The arenas in Europe actually have a much bigger floor area too as most of the US venues are basketball layouts .
The more likely reason I can think of U2 preferring the US is that Livenation the U2 promoter own alot of the venues in the US so they can get a bigger cut of the profits .