The publishers didn't sue without the NEL; they had lots of opportunities, but CDL wasn't worth the fight to them. Shortly after the NEL, they sued. It's clear

The publishers didn't sue without the NEL; they had lots of opportunities, but CDL wasn't worth the fight to them. Shortly after the NEL, they sued. It's clear that the NEL was the triggering factor. From publisher's/authors' perspectives, there is a massive difference between "controlled digital lending but we respect copyright" and "digital lending, and we can choose to dispense with copyright restrictions whenever we think it is justified". One of those was an uneasy peace, based on the idea that IA - while it disagreed with the publishers on some issues - was at least acting in good faith. The other one would essentially have gutted all copyright protections, making respecting IP rights purely a matter of choice. Whatever you think of IP and copyright as a whole, publishers were never going to accept that massive change in approach.