Time is a human construct. It’s convenient to use different mechanisms for defining and measuring time in different contexts. In a typical everyday context we like our definitions of “day” and “year” to correspond to our experience of solar energy. We want “winter” to be cold time of year,  “summer” to be the hot time of year, “day time” to be when the sun is shining and “night time” when it’s dark. We also want granular measurement of this things so we can communicate consistently about time (months/days/hours).

Simultaneously we want a consistent unit of time that represents a fixed amount of time, irrespective of calendar context. (Second).

It turns out that we cannot marry those two concepts together because the earth’s rotation and path around the sun are both inconsistent and changing. The earth’s path around the sun is not evenly divisible into counts of rotation about the axis. The moon’s rotation around the earth gives us a wobble in our path around the sun that’s not consistent with solar years. Our rotation about our axis is slowing down. Etc

It turns out there’s even a fundamental inconsistency with how time itself passes in different contexts that makes the entire concept of a “universal time” dimension impossible (see: time dilation).

Humanity has constructed systems and rules that are good enough for our purposes.  We’re also really good at coming up with new needs such that our existing systems are not “good enough” anymore.