“Project Panama is our effort to destructively scan all the books in the world,” an internal planning document said. “We don’t want it to be known that we are working on this.” ..."
They do this because the law required it.
And since when do AI companies care about copyright law ?
> After the initial transfer of ownership of a legal copy of a copyrighted work, the first-sale doctrine eliminates the copyright holder's right to control ownership of that specific copy.
As near as I can tell, there is no legal pressure for them to do that. They're destroying them because that's how their scanning machinery works.