I've been in the US 7 years and I haven't quite yet understood why credit cards companies and banks are separate entities. (regulation?)
However credit cards do exist, even if they have been maligned for a long time in media:
Major credit card issuers in France are often linked to the retail sector (see http://www.pass.fr) .. others got consolidated into traditional banks (cetelem for example)
The traditionally French "no permanent credit" model for banks tend to raise fees and favour low deposits I guess.
In both cases anyway the banks pray on the poor / moderately poor people to "dress them up" with all sorts of products and credits they don't need. (And arguably, that society pays up after 30 years)
So when credit cards came around, it probably wasn't an existing bank saying "maybe we'll let people go negative and then charge them huge interest"; it was a separate entity offering people what essentially is a way to be conveniently loaned money.
They probably just never integrated into 1 entity.
There may be regulation as well, but none that I know.