If they bought physical books then the lawsuit might happen, but it would be much harder to win.
If they bought e-books, then it might not have helped the AI developers. When you buy an e-book you are just buying a license, and the license might restrict what you can do with the text. If an e-book license prohibits AI training (and they will in the future, if they don’t already) then buying the e-book makes no difference.
Anyway, I expect that in the future publishers will make sets of curated data available for AI developers who are willing to pay. Authors who want to participate will get royalties, and developers will have a clear license to use the data they paid for.