six under 3.31.4 not done since 2015, only 5 times in history, 3 in monaco.
Why can't U.S. guys run sub 3:30 regularly?
Because no one does it regularly, and only one country does it with some semblance of frequency.
One country as in Kenya? Morocco is very close, they have 40 and 34 sub-3:30 performances, respectively. All other countries together only 25, crazy to think how dominant those two have been at this event.