Again, you're assuming a lot about this situation that we don't actually know to be true. For example, that these purchases are limited to "bargain bin" books that have essentially no market value. These may be cases we know about, that doesn't mean these are the only purchase happening. I would hypothesize that if we know about a few specific purchases there are probably many more we do not know about/haven't traced back to these companies.
You realize "market value" isn't the only kind of value too, right? Even books that are completely obsolete can have inherent historical value insofar as they enrich our understanding of the past and how human beings used to live. Contemporary market value isn't everything. There are plenty of works of scholarly interest that wouldn't command nearly requisite value to a NYT bestseller when you adjust for scale. That doesn't mean these books aren't worth keeping or aren't intellectually important.
Also, these books presumably even have some perceived value, otherwise these companies wouldn't think they were relevant for training, and wouldn't be spending money to purchase and scan them in the first place. The whole premise is that these books are valuable enough such that training on them will make the models valuable and make paying customers line up for tokens. This is an inherent imputation of value to these works on the part of these companies. You can't say, simultaneously "these books are worthless" yet somehow, at the same time, "they are worth something for producing artificial intelligence". Your assumptions don't make any sense.
> They're books that are no longer in print. Doesn't mean there aren't a lot of copies around.
Sure, but there also could be limited copies around. We don't know. We won't know unless these companies are more transparent about exactly what they are buying and scanning. It's that simple. If it's foolish to assume there might be limited copies, it's equally foolish to assume they have plentiful copies. We simply don't know.
> Nobody has an obligation to spend money to preserve every extant copy of every book forever.
I don't think anyone is claiming that. People are bothered because they (in my mind, rightly) recognize that old books are a historical record of human accomplishment and have some amount of cultural value. Letting a handful of companies further plunder the collective output of humanity and now, potentially keep it locked on their servers in perpetuity is something that should make you upset if you have any inkling of interest in the history of humanity or human accomplishment and if you have any sliver of curiosity about these things. If all you care about is the present and getting better LLMs, sure, I guess I understand why you don't care, but then I also think you are very unwise and myopic.
> Millions of books are destroyed everyday.
So what? Millions of crimes are committed every day, that doesn't mean we shouldn't be bothered by the crimes we hear about. Billions of pollutants are spewed into the environment every day. That doesn't mean we shouldn't try to combat pollution. That's a pathetic attempt at justification. Also, there are clear distinctions between processes like libraries removing works they can no longer store and companies scooping up books for training and personal gain.