> By that logic they should ban gift cards and in-game currency too.
When you buy a $10,000 TV on a credit card, and can't make your payments, you're an idiot. There are a lot of idiots, but very few of them will do impulse purchases like that - because they understand that next month, they'll have to pay for it.
When you invest $10,000 of money that you pulled from a credit card... People feel completely different about that. If you have confidence in your investment, why not borrow money to fund it? You'll make that money back, and pay the debt off! If you don't have confidence in your investment, you wouldn't be investing anyways, with your own dollars, or borrowed ones.
Investing self-selects people who are (unreasonably) confident in the return rate on their investments. This is why you can't buy stocks or bitcoin on a credit card, but you can buy Magic: The Gathering cards.