Like, I really don't know what people objecting to this imagine typically happens to old, unwanted books. They don't get sent to some magical library in the countryside if unpurchased where they are carefully maintained forever (next to where Rover spends the rest of his days). They are very literally thrown into the trash.
That said, I'd be thrilled if the US government required AI companies to make them available to the public. I'd even settle for the US government making it legal for them to.
In the UK at least, people usually take them to a second hand / charity shop, who sort through them and send the valuable ones to auction (typically early editions, 100+ years old) and then either sell them themselves (for recent books that are easy to get rid of) or sell them to specialised second-hand bookshops.
Most of the specialised second-hand bookshops rarely throw books away, usually if nobody buys them after a couple of years they end up in the extreme discount piles (20p, 50p etc) and probably only trashed if they still don't sell from there.
I do get the _idea_ of preserving books, but... people don't care. I just threw out well over a thousand books from my grandparents house this spring.
There were ~6-10 "valuable" books there. Two because I personally knew someone who wanted old war-time books and a few 100+ year old bibles. And maybe two dozen books worth saving, mostly because they were from big-name authors or had stuff that nobody would print anymore (I have detailed instructions how to make laughing gas and how to build an underground chemical lab - hobby books in the 50s were ... interesting :D )
I literally couldn't give away the rest. And I tried. It was all just "interesting, but..." - no way to justify using the shelf space for books that, realistically, nobody will actually ever read again.
There are also other weird issues such as the UK having a clause protecting Peter Pan (so a children's hospital gets royalties) and the King James translation of the bible (under Crown copyright) that extend the copyright even further.
In short, it's a mess.
At the same time I can understand keeping track of when each books enters public domain might also be an absolute nightmare, and I wouldn't blame the AI companies for not wanting to deal with that. For the stuff they absolutely know is clear, they should provide dumps for everyone to download.