Okay, the Kinder Surprise isn't banned in the US just because it's considered a choking hazard — it's actually a deeper problem than that. See, the 1938 law that established the FDA (to stop things like the incident in 1937 where a drug company killed a bunch of people because they didn't look up what they were mixing their medication with) has a bit that bars food companies from packaging non-food things inside food. (With exceptions for structural things like popsicle sticks.) So it's not a case of looking at a product and making up rules, it's applying pre-existing rules.
Laws can change, of course — but it turns out the reason they're still banned is that back in 1997 Nestle tried to launch "Nestle Magic", a Kinder Surprise knockoff, knowing it was illegal and launching a big advertising and lobbying campaign after putting it on shelves. Since the thing everybody hates most is a smartass, they lost big and were forced to take it off the market, thus poisoning the legal environment for Kinder.