Because Liberapay is legally based in France, we only have access to three card networks through Stripe (Visa, MasterCard, American Express), whereas a US-based platform also has access to four others (Discover, JCB, Diners Club, UnionPay).
It looks like platforms based in France can now process card payments through one more network than US-based platforms, so I'm closing this issue as obsolete.
Because Liberapay is legally based in France, we only have access to three card networks through Stripe (Visa, MasterCard, American Express), whereas a US-based platform also has access to four others (Discover, JCB, Diners Club, UnionPay).
This is visible in Stripe's pricing page. France:
US: