Actually, you can, but it can be kind of unwieldy. You can use your credit card at several sites, such as coinbase.com and coinmama.com, and supposedly changelly.com, and you can even redeem all kinds of gift cards, as well as use your credit card, at paxful.com. Of course, in addition to being unwieldy, some of these sites can also hit you with a significant premium, but at least you'll be able to get your hands (metaphorically speaking) on some cryptocurrency!