IMO It's an Antitrust issue as well besides releasing any NDA/confidential settlement agreements will affect current and future pending lawsuits. Remember,Antitrust limits complex patent settlements. Patents, patent litigation, and patent settlements increasingly influence competition. Settlements of patent disputes may come in many forms, including but not limited to licensing and cross-licensing agreements, patent pools, mergers, and joint ventures.

While frequently pro competitive, such settlements can stifle competition and harm consumers. There is a specific antitrust rule that limits such settlements i.e. a settlement must leave consumers at least as well off as they would have been from ongoing patent litigation.

After establishing that profitable settlements satisfying this constraint generally exist, antitrust rule can be used to evaluate mergers, patent pools, and negotiated entry dates that settled infringers would never release and so they do NDA's.