I saw a report on twitter with serial numbers showing build dates of September and November, along with old copyright dates on the boxes on the new AirPods. Combine that with the "Hey Siri" being shown in "Gather Round" video in September, I bet they were hoping to ship the AirPods before the holidays, but were holding out hope that Airpower would work.
https://twitter.com/rouven81/status/1110980080170340352 https://www.macrumors.com/2018/09/12/apple-hey-siri-support-...