I've taken three kids out there other the years from the east side of the country. The weather seems like it's perfect every year. Travelling to a meet, especially across the country, is always exciting for kids and gets them even more focussed than normal. The primary goal is to run fast, winning is almost secondary. It's not like a state championship where the title matters most.
This year 18 of the guys in the race had already one at least one state championship. Most of these guys go into their state championship as favorites. They're expected to win there. Anything less than a win would be a massive disappointment.
At Arcadia, few have such expectations so they are freer to take risks and let it rip.
Furthermore, everything about that meet is set up for record breaking performances. They change the directions of sprints to give the greatest chance at setting records or creating top performances in the US. By the time the 3200s run, the environment is absolutely electric.
Like Footlocker it's also a great opportunity for elite kids to race other kids they will likely see in major races in college.
Having the New Balance meet in the southeast in June just isn't conducive to great times, so I doubt there will ever be many years where the 3200 at Nationals is near as deep as Arcadia. The exception might have been 2007 when Centrowitz and Forys went at it at Nationals. The Adidas and Brooks meets are also siphoning off talent at that time. Aracdia is like a perfect storm for elite 3200s.