If you've read the articles covering this issue, you'll be aware the concern is over the fate of rare and out of print books, rather than your straw man (ie those available in 'thousands to millions' of copies).
https://www.bbc.com/news/articles/cp3rprx2wl4o
> "A recent academic text published in only 100 copies, 75 of which are already in libraries, may be very rare on the market - but it is perhaps not such a great loss if one copy is destroyed," says Derek Walker, owner of Edinburgh bookshop McNaughtan's.
> "But we have, and have sold, books which are for example the only known surviving example of an edition from the 18th century.
> "It would be a much more significant problem if one like that were to be bought for destruction, having survived this long."