[teraflop]

That's not really true, unless the only things you buy with your credit card are services and perishable goods.

The credit card companies' business model is similar in some ways to insurance. They skim a bit off the top of each transaction, and in exchange they bear various kinds of risk. One kind of risk is default/bankruptcy, as another commenter has mentioned. There's also the problem of fraud: since cryptocurrencies make it relatively easy to launder money, a Bitcoin purchase is disproportionately more likely to be fraudulent, even if the account is otherwise "in good standing".

(Note that it may also make sense to discourage or disallow gambling on credit for public policy reasons. For example, a number of states already prohibit the sale of lottery tickets using credit cards, even though those tickets have a non-zero expected value.)

[gowld]

Credit card companies main business is in transaction processing (both for customer-vendor transactions, and for helping banks administer these revolving loans to customers). The insurance is one feature, not the whole model.