Because there is no such thing as a "global citizen", first of all. And just taking a look around, the death of the nation state must've been greatly exaggerated in some circles.

>these experts are most likely paying taxes at the top tax bracket.

Who cares. This is a thinly veiled attempt to say that any person's worth in a given society is approximately equal to how much they pay in taxes - which is insane, for a great many reasons.