The careless errors of credit reporting agencies
The US is as far as I know the only country in the world who have a positive creditscore system.At least in Europe it's mostly based on a negative creditscore i.e. you are trusted by definition but if you don't pay your bills you end up not being allowed access to credit.In the US they don't trust you per definition and instead you have to prove that you are good with money by basically creating debt and then paying it off.This is obviously to say the least absurdly backwards, but I believe there is a rational explanation and that is that the US is a country of immigration and so you had to find a way to allow foreign people without any history and no reason to trust them.