If I had to guess, I'd say it's probably just because that's how it always has been. Bank accounts where you put your money and loans have always been separate.

If I had to guess, I'd say it's probably just because that's how it always has been. Bank accounts where you put your money and loans have always been separate. 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.