The iPhone is really big in Japan (it's one of the few countries where it has a higher market share than in the US) which probably makes it more worthwhile for Apple
That doesn't make any sense. It's supported on local phones for both iOS and Android. What iOS does that's special is enable FeliCa for all regions globally. It only affects people from outside Japan traveling there.¹
Since it's not free for them, I assume they determined the amount of people in their key demographic that visit Japan was worth providing a stellar experience. Considering 2.7 million Americans visited last year, it was probably a bet that's paying off.
¹ Or, incidentally, people who live there but purchase phones overseas to avoid an obnoxious camera shutter sound forced on at all times.
I do wonder who it is that has all of these android phones in the US (nearly 40% by the statistics). In my extended friend group only one person other than me uses an Android phone.
People who can't afford to spend $599 on a phone. Or those who can afford it but can send picture messages all the same on a phone that costs hundreds less.