Why? Most of the big porn studios are as trustworthy as any other Internet business of the same size, and if your credit card number is misused, you're not liable for the charges anyway. Porn popularized selling DRM-free content for money long before Louis CK made it popular. Porn actors need to pay their rent too.
The probability of a leak may be similar but the downside isn't. It's no problem whatsoever if your name is linked to cheapprogrammingbooks.com, you cancel the card, get a new one. The situation is somewhat different for spermgarglingteens.com.