If they have the sponsor money and ego to go there. Actually US riders have made some improvements in performance to be in the same time zone. Logan Owen, the U-23 guy is a great crit rider and reasonable road racer. Given time and continued self-abuse he could be a really good CXer. Hope he comes to his senses, soon.
I know you're exaggerating for effect, but still, that's a bit harsh. Top American has only finished outside the top 20 twice in the last 10 years. And we've got Worlds podium contenders in the Junior Male and Elite Womens divisions.