This assumes, based on the actual evidence, that the set of people who buy cryptocurrencies on credit are more likely to default on them than a set of people with the same credit ratings buying sofas (and that raising APRs to cover these increased losses will have other adverse affects on a credit card company's business).

If people are speculating beyond their means in crypto because they think the line of easy credit gives them a means to make a profit out of it, it's far easier for everyone involved to just cut the line of easy credit for the crypto, because the same person is probably not going to try to make a profit loading up their card with consumer goods or cars or other things the credit card company doesn't mind extending credit for instead.

I really don't understand why you believe it is reasonable or preferable to oblige credit card companies to take losses instead.