Why do people say Costco croissants are not real croissants? Whats the difference?

Well, I've never tried Costco croissants, but there are a lot of poor imitations of croissants out there. Real croissants are fantastic, made with er (not vegetable fat or artificial ingredients) and have fine layers of flaky pastry. 'Not real' ones may look similar but they are much more bread-like in consistency and not particularly interesting. Supermarkets and companies get away with selling cheap imitations because many people do not know what proper croissants are like. In the UK, only Delices de France does good croissants and you can buy them in local cafes. Supermarket croissants are useless (Tesco, Sainsbury's).