Seems like track & field, boxing two former sports where America dominated and was a past time is now losing the public interest and ability to attract the young.
That's not the case for boxing. In regards for boxing, there is so much money to be made now, the traditional route of "Become an Olympian, win a medal, sign with a big promoter" isn't the only way to make millions. In fact, if you're an amateur who is already at the ceiling of how good you can be at that level, it's straight up foolish to wait a whole Olympic cycle. Unless you're peak at the am level coincides with the Olympic cycle then there's no point.
On top of that, promoters are now more active and aggressive in signing amateurs before they get to the Olympics. The incentive just isn’t there for American boxers to go through the process. It’s completely the opposite for foreign fighters, as this is their only way to get on the map and Olympic programs will keep paying them. More than they’d make trying to make it out of their small local circuits until hopefully hitting it big with one of the few major European promoters or in the US.
Danny Garcia, Mikey Garcia, Adrien Broner, Terrence Crawford and others, all amongst the top talent currently in or entering their prime in the pro ranks, all current or former champions, all passed on the 2008 Olympics to get a head start on their pro career.
Plus, Olympic judges love robbing US boxers.