It's not that there are more Americans, it's because more actual countries use the ANSI layout.

I'm in the UK, but dropped ISO years ago in favour of ANSI. I don't need to worry about whether a keycap set supports ISO... or a keyboard for that matter. I also don't have to put up with the ridiculously tiny left shift key either. I also think ISO looks crap and unsymmetrical, but that last one is just personal preference.