Magnetic RCA adaptors: Latest snake oil?

Just a silly question, "Why would you want to introduce a magnetic field into the electromagnetic field around your cables?"

Because the magnets cause the magnetic field to leave at a right angle to the wire.

Probably, but I remember years ago when I moved by outboard transformers for some old
PS Audio power amps and told my favorite salesman (very timidly, since I didn't want to make it sound like I heard the huge difference that I had heard).  He told me that he'd been in the business 20 years at that point and if I "told him the amps got up and marched around the room",
he'd believe me.  You never know until you try, but some tries cost more than others.

The vector of the induced magnetic field in the cable, the one produced by current flowing through the cable, IS at a right angle to the cable. So one wouldn’t need anything else to cause it to do that. So it must be something else.

Again, I suggest reading Dudley's article, it includes a description of Ric Schultz's design and what he claims it does. While it made things worse in Art's system, he didn't discount that it might work in other systems.