It's a very strange definition. Would you consider domestic chickens "endangered"? Clearly if there are many kept in captivity and bred, there's little chance of them becoming extinct even if there are nearly none in the wild.
Do you also find it strange that e.g. various wolves are/have been considered endangered even though dogs exist?
I suppose it's because we assume "endangered in the wild" means something that doesn't breed well in captivity and so is hard to reintroduce.