alt Hacker NewsFun fact, two (very expensive) wristwatches have actual atomic timekeeping in them, instead of just receiving a radio time signal: the Bathys Hawaii Cesium 133, and a few different shaped from Hoptroff London.
All released 2013-2015. Not sure what happened then for there to be suddenly two.
Symmetricom (now owned by Microchip) released the first Chip Scale Atomic Clocks in 2011. It probably took some time for them to become available to watch designers and for them to be integrated into watch designs.
https://www.nist.gov/noac/success-story-chip-scale-atomic-cl...
I'm guessing the watches sold poorly and the chip packages are still large compared to a watch movement, so no new designs.