The NN has copyright material stored (maybe in compressed form) inside of it. That's quite literally the definition of copying, and if you do that without licence copyright infringement.

Note how software licences typically give you the licence to make a copy for running the program? That's because the act of copying the program from the medium (cd, USB stick, HDD...) is considered copying.

I really don't understand what's so difficult to grasp about this. And yes it is illegal to sell equipment whose purpose is circumventing copyright protections.

I don't know US, but if similar to Australia then you can sell the machines, but there are specific regulations regarding public access to them, which boils down to posting notices about copyright violations and passing liability onto the user. Because apparently a stern warning stops students from photocopying expensive text books. Which is the sort of thing Midjourney and OpenAI will be relying on for their defense, yes.

It is also interesting that there are technology specific laws. You can't sell photocopiers to the public capable of reproducing bank notes for example. Or taxes added to blank medium such as cassette tapes.