That’s a very recent change - and it’s not like 9192631770 transitions/hz (which is hilariously self referential!) is some obvious, natural value that ISN’T based on the historic ‘typical’ length of the day based on our rotation around the sun.
A second being 1/86400th of a day (24 hrs * 60 minutes * 60 seconds per minute) is still essentially true, and based, essentially still on the seasons and our movement around the sun (or relative movements between the various bodies in the solar system, depending).
Being a chaotic natural system, we of course need to add fudge factors here and there to simplify the math day to day while keeping it aligned with observed reality, like leap seconds and all), at least where it intersects with reality in a material way.
A second being 1/86400th of a day (24 hrs * 60 minutes * 60 seconds per minute) is still essentially true, and based, essentially still on the seasons and our movement around the sun (or relative movements between the various bodies in the solar system, depending).
Being a chaotic natural system, we of course need to add fudge factors here and there to simplify the math day to day while keeping it aligned with observed reality, like leap seconds and all), at least where it intersects with reality in a material way.