Received wisdom suggests that any 12 of the top 40 players at the U16 trials should be able to win gold ... and easily. Clearly, however, that did not happen, so the first question to me would be
Was Brazil really that good?
There was a time when Brazil's national team was a world power, and in fact beat the U.S. in the 1994 World Championships behind Hortencia and Magic Paula, so it's possible that there's talent enough again.
Or it could be that Dori Oldaker did a terrible job of coaching, which is almost impossible to know unless you're at practice every day. It could have been one really bad day for a team that otherwise did fine, or it could have been an example of how poorly she led the team. (Oldaker, by the way, has had a great career at Mt. Lebanon HS in Pennsylvania, so it's not as if she's some rookie who had no clue.)
Or it could be that the American players in this year's crop weren't up to previous standards, and there just wasn't as much talent as before.
Or, most likely, a combination of all three, plus maybe some chemistry issues.
Regardless, a nasty black eye for all involved ...