Wallets may have characteristics such asmoney clips; a coin purse; a chain fastener, strap, or rein; or a zipper. Specialized wallets are designed for holding passports, wearable ID cards, and checkbooks to give some examples.
A card holder won't bulge excessively when filled with loose change and can also be easier to access in your front pocket, rather than being thrown into a bag, rucksack or backpack. Naturally it's small size will accommodate only what it fits, which is less than a wallet.