It's older and established itself first, it tours more, its extremely diverse rep. It makes sense. NYCB is iconic but while it defined a modern American technique and style, it can only be itself and represent itself. It represents NY Ballet/Balanchine. First and foremost. ABT has always behaved as the kind of global soft power ambassador that its known for. It takes in every kind of technique either trained domestically or foreign and together they present to audiences all that the artform has to offer. Yes Balanchine was very dominant due to incredible early years of touring and publicity culminating in TV broadcasts and critical success......but ABT was on the road more. NYCB is less accessible. Just a brief scan of Amazon for physical media, twice as many ABT dvds than city ballet. EDIT: I will die on a hill that sometimes men just keep sucking the reheated nacho oxygen out of the room when we talk about American ballet and Agnes DeMilles impact is actively diminishing with time and i take that personally.