Här finns lite info från tillverkaren av en smartwatch med ungefär samma SoC och pris, PineTime:
As you have noticed if you've paid attention to our announcements, the PineTime is rather small and very affordable. This requires some compromises in hardware. The chips that we use in our existing platforms (Allwinner A64, Rockchip RK33xx) are far too large dimensionally and consume too much power to be practical. "Big-name" smartwatches such as the Apple Watch and Samsung Gear use cut-down and low-power relatives of normal smartphone SoCs, which could run Linux (and do, if you count Android). However, these chips would heavily increase the price point and tend to not be very open-source friendly.
Så det finns nog flera faktorer som spelar in valet av SoC: pris, strömförbrukning och tillgång till öppen källkod.