One can be a tiny bit more charitable and say many of them provide a nearly worthless service (slapping your manuscript on their fly-by-night website) while misrepresenting themselves as providing a much more valuable service (peer review, dissemination to an audience that actually reads their journal, etc) and charging accordingly (thousands of dollars per manuscript).

Perhaps it's arguable whether that is to be called a scam, but certainly it is a rip-off.