Presumably they aren't ('sold legally') - in the same sense that exceeding the speed limit, robbing a bank or murdering one's life may not (even cannot) be done legally.
Being 'illegal' and 'never happening' are obviously two different things - which, in the real world, do not necessarily come together.
The impression I get is that at one extreme there are items that are explicitly illegal, and at the other extreme there are products a legitimate seller with lots to lose would be happy selling. And that in the middle there is a huge grey area. Stuff that is not expicitly illegal, but your lawyers/insurers would neverthless advise you not to sell.
In general, the same connector can be and often is used for multiple applications. An adapter that may be perfectly safe in one application may be highly dangerous in another.
Unless there is some law explicitly forbidding "misuse" of IEC 60320 connectors it's difficult to see how these adapters would be illegal.
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