Do you also have bags of asbestos, buckets of leaded paint, poof your hair up with black market CFC hairspray, maybe decorate with radium glowing clocks?
If these magnets are used incorrectly, why should the responsibility for that not be the users?
As far as your question, I've spent enough time with corporate legal to know many of these protections are industry driven to scaffold up a legal framework to protect themselves.
That's what "self regulation" actually looks like in material reality. I wouldn't be surprised if that's what was done here.
It's producer protection - doing say $100mil in sales on a legally grey product makes attorneys nervous
The resulting government policies are usually a direct result of multiple cases in civil litigation.
The libertarians rules have been followed. Some of them just really don't believe in what they preach.