Possibly because the patents were invalid due to the existence of prior art? Previous discussion: https://news.ycombinator.com/item?id=15875685
According to the article, the infringement claims were dropped after Waymo was notified of the USPTO reexamination that was going to be done due to Swildens filing the ex parte reexamination request.
>...So he took the unusual step of challenging the 936 patent himself, filing what is called an ex-parte reexamination request. He gathered the prior art he had discovered, completed reams of paperwork, and pulled together his detailed arguments into a 101-page document that he filed with the USPTO on August 1.
Waymo dropped the claims relating to the 936 patent on Sep 13.
>...Swildens, naturally, thinks his reexamination request played a role. He notes that USPTO had a phone interview with Waymo’s lawyers a few days before, on September 8, at which the examiners presumably told Waymo that a reexamination of the 936 would be going ahead. If the reexamination started while the patent was being actively litigated, Uber and the court would have to be informed.
https://www.wired.com/story/eric-swildens-uber-waymo-lawsuit...
What was supposed to be the original slam dunk for Waymo, 'trade secret 96', Which referred to PCB circuit diagrams that were accidently emailed to Waymo instead of Uber ATG by a shared supplier, was even dropped. Waymo's whole case was pretty flimsy.