It seems to me that if some anonymous ne'er-do-well were to publicly re-host the model files for separate download; and you acquired the files from that person, rather than from Google; then you wouldn't be subject to their license, as you never so much as saw the clickwrap.
(And you wouldn't be committing IP theft by acquiring it from that person, either, because of the non-copyrightability.)
I feel that there must be something wrong with that logic, but I can't for the life of me think of what it is.
Google gives the model to X who gives it to Y who gives it to Z. X has a contract with Google, so Google can sue X for breach of contract if they violate its terms. But do Y and Z have such a contract? Probably not. Of course, Google can put language in their contract with X to try to make it bind Y and Z too, but is that language going to be legally effective? More often than not, no. The language may enable Google to successfully sue X over Y and Z’s behaviour, but not successfully sue Y and Z directly. Whereas, with copyright, Y and Z are directly liable for violations just as X is
Now, if you are aware of a contract between two parties, and you actively and knowingly cooperate with one of them in violating it, you may have some legal liability for that contractual violation even though you weren’t formally party to the contract, but there are limits - if I know you have signed an NDA, and I personally encourage you to send me documents covered by the NDA in violation of it, I may indeed be exposed to legal liability for your NDA violation. But, if we are complete strangers, and you upload NDA-protected documents to a file sharing website, where I stumble upon them and download them - then the legal liability for the NDA violation is all on you, none on me. The owner of the information could still sue me for downloading it under copyright law, but they have no legal recourse against me under contract law (the NDA), because I never had anything to do with the contract, neither directly nor indirectly
If you download a model from the vendor’s website, they can argue you agreed to the contract as a condition of being allowed to make the download. But if you download it from elsewhere, what is the consideration (the thing they are giving you) necessary to make a binding contract? If the content of the download is copyrighted, they can argue the consideration is giving you permission to use their copyrighted work; but if it is an AI model and models are uncopyrightable, they have nothing to give when you download it from somewhere else and hence no basis to claim a contractual relationship
What they’ll sometimes do, is put words in the contract saying that you have to impose the contract on anyone else you redistribute the covered work to. And if you redistribute it in full compliance with those terms, your recipients may find themselves bound by the contract just as you are. But if you fail to impose the contract when redistributing, the recipients escape being bound for it, and the legal liability for that failure is all yours, not theirs