Assuming that books used for GPT training were indeed purchased, not pirated, and since "AI training" was not prohibited at the time of the purchase, the engineers had every right to use them. Maybe authors in the future could prohibit "AI training" but for the books purchased before they do, "AI training" is a fair usage.
Ownership is never absolute. Just like with music - you are not allowed to use it commercially i.e. in your restaurant, club, beauty salon, etc. without paying extra. You are also not allowed to do the same with books - for example, you shouldn't share scans online, although it's "your" book.
However, it is not clear how AI infringes on the rights of authors in this case. Because a human may read a book and produce a similar book in the same style legally.
I agree, the ownership is not absolute.
However, just as a person does not own the work of an author, the authors do not own words, grammar, sentences or even their own style. Similarly, they do not own the names of the characters in their books or the universe in which the plot is happening. They even do not "own" their own name.
So the only question remaining becomes whether is AI allowed to "read" a book. In the future authors might prohibit it, but hey, we're just going to end up with a slightly more archaic-speaking GPT over time because it will not train on new releases. And that's fine by me.