Unfortunately, electronic devices come with quartz crystal resonators, or rubidium or cesium resonators. After frequency calibration these will keep stable time relative to the atomic clock timebase.

There is no device available that allow you to derive a clock from the relative motion of the sun about the Earth’s axis, such that the changing definition of days and seconds relative to realizable clocks can be tracked.

Furthermore it’s kind of nice to have a stable and standard definition of seconds and days. For instance, under the “ut1 system” you don’t know how long a present second is until the present day’s final observations are made.