There are two reasons. I like the arrival time - I get to the hotel around 1pm and most hotels will usually find a room at that time (and on this occasion I had a guaranteed midday check-in) which gives me an almost full day in the city. And it used to be the case (or so it seemed) that it was the first flight of the day into T7 and hence no queue at immigration. However it now seems there is a flight from Tokyo arriving around 15 minutes earlier (although JFK immigration was still not as painful as many describe - about a 20-minute wait which is no worse than LHR was for UK citizens on the return).