Unlike the (solar) day and year and the (lunar) month - the week (of seven days) is a socio-cultural construct of arbitrary length - presumably derived from the Christian, and before that Jewish, religious cycle.
But nowadays when societies have become secular and abandoned the week-long cycle of most churches; and almost every vestige of the weekly cycle is obliterated for a substantial segment of the population (e.g. those who do not work, do not attend educational institutions or whose work timetable includes all weekdays) - the arbitrary nature of the week is becoming very obvious.
Of course, our modern non-lunar months are also arbitrary - and most people have no awareness of the lunar cycle (I mean literally no awareness - zero knowledge).
All this, I feel, adds to our alienation and dislocation from the world - I mean that our world is governed by (what are perceived) as meaningless - but strictly and universally enforced - divisions of time.
Note added - A correspondent writes with the plausible theory that the week is approximately a quarter lunar month - and that the quarter phases of the moon have long been of interest to humans.