A DMCA takedown is a tool for a very specific situation, where a small-time, difficult-to-identify, near-anonymous user uploads copyrighted content to a third-p

A DMCA takedown is a tool for a very specific situation, where a small-time, difficult-to-identify, near-anonymous user uploads copyrighted content to a third-party, big-time, easy-to-identify host. The copyright owner would prefer to sue the original uploader, but suing the host is a lot easier, so the host is strongly encouraged to obey the DMCA takedown as quickly as possible. In this case, the uploads were done by the Internet Archive itself, not by a near-anonymous user. So there's no point to sending a DMCA takedown - the copyright owner already knows the identity of the original uploader, they're easy-to-identify and they have money to pay damages. Therefore, they're just suing the IA directly.