It just doesn't work like that for international sports tournaments. During the Doha 2006 Games, whole teams would arrive at the airport with one passport and no visas between them. The organisers were meant to arrange the visas, but something went wrong. The authorities were flexible enough to get the teams through.
This is probably what happened with this event. The US team were invited, but the organisers couldn't get visas, or forgot to get visas for the competitors. Because of the current political tensions, the Tehran government isn't prepared to show any flexibility to make the event a success.
It just doesn't work like that for international sports tournaments. During the Doha 2006 Games, whole teams would arrive at the airport with one passport and no visas between them. The organisers were meant to arrange the visas, but something went wrong. The authorities were flexible enough to get the teams through.
This is probably what happened with this event. The US team were invited, but the organisers couldn't get visas, or forgot to get visas for the competitors. Because of the current political tensions, the Tehran government isn't prepared to show any flexibility to make the event a success.