Apparently it's a FIFA rule to ratf*** the IOC
Why FIFA blocks the U.S. men's national team from playing for an Olympics spot
The US had plenty of good U23 players on the A squad due to the INTL break since FIFA required their release. But the "age-group" designation given to the Olympics by FIFA (again, ARBITRARY) simply treats the Olympics differently in order to water down the product and protect the World Cup.
Pretty shitty.
Then they allow 3 exceptions which is a wink-and-nod to the powerhouse countries who undoubtedly will make the Olympics and rebel against FIFA if their top stars aren't allowed to compete.
I get that other countries can work around this somehow but the USA doesn't have the depth. We're going to be screwed for a long time unless something changes, either in the pipeline or in the way we approach it.