Calendrical idiosyncracies make far more sense when you realise that:
1. They refer to three distinct and largely independent phenomena: the rotation of the Earth about its axis (day, and subdivisions hours, minutes, and seconds), the orbit of the Moon around Earth (month, with caveats), and the orbit of Earth around the Sun (year). The fact that there is a rough days-based approximation of each is coincidental. Consider that on some planets there is no clear definition of a day (e.g., gas giants with no observable solid ground), or fixed rotational period (the duration of Venus's "day" apparently varies considerably under the influence of winds, and even Earth's day changes measurably due to tidal influences and factors).
2. Collective agreement and tradition are a real bear. It took nearly 500 years for the Gregorian Calendar to be universally adopted --- Russia's "October Revolution" occurred in what most of Europe considered to be November, as Russia had not yet adopted the Gregorian Calendar first introduced in October 1582. And it wasn't even the last country to do so! China's adoption of the Gregorian Calendar occurred in the 1940s. Calendrical decimalisation has been attempted, particularly notably during the French Revolution (amongst the same reforms which brought us the Metric System), as well as in the USSR. Switching to a ten-day week was exceedingly difficult given a) the traditions of seven-day cycles, particularly in religious contexts, as well as an external world based on the seven-day week.
1. They refer to three distinct and largely independent phenomena: the rotation of the Earth about its axis (day, and subdivisions hours, minutes, and seconds), the orbit of the Moon around Earth (month, with caveats), and the orbit of Earth around the Sun (year). The fact that there is a rough days-based approximation of each is coincidental. Consider that on some planets there is no clear definition of a day (e.g., gas giants with no observable solid ground), or fixed rotational period (the duration of Venus's "day" apparently varies considerably under the influence of winds, and even Earth's day changes measurably due to tidal influences and factors).
2. Collective agreement and tradition are a real bear. It took nearly 500 years for the Gregorian Calendar to be universally adopted --- Russia's "October Revolution" occurred in what most of Europe considered to be November, as Russia had not yet adopted the Gregorian Calendar first introduced in October 1582. And it wasn't even the last country to do so! China's adoption of the Gregorian Calendar occurred in the 1940s. Calendrical decimalisation has been attempted, particularly notably during the French Revolution (amongst the same reforms which brought us the Metric System), as well as in the USSR. Switching to a ten-day week was exceedingly difficult given a) the traditions of seven-day cycles, particularly in religious contexts, as well as an external world based on the seven-day week.
A great book exploring the history of the (mostly) universally-adopted Gregorian system is Eviatar Zerubavel's Seven Day Circle: <https://openlibrary.org/works/OL1962761W/The_seven_day_circl...>