I wouldn't say it sucks them out of karts way too early. Some of them may have been keen to race GT cars rather than Formula 1, and if that's the case then getting into cars as soon as possible can only be a good thing. Besides, you can start racing karts from, what, 8 years old? And you can compete in the Ginetta Juniors from 12-17 (correct me, that's a rough guess), so you could have at least 4 years of karting experience, probably a couple more.
Of course they haven't had the chance to race the 'professionals over in Europe', half of them are barely teenagers. Give them a chance!