Not all countries chose the same days for weekend and work days. Some Arab countries had Thursday – Friday as their weekend, but this has shifted to Friday – Saturday to align better with US/Europe etc.
Friday is the religious day of the week for Muslims, like Sunday is for Christians, so naturally they prefer to have that day off.
The Catholic Church set aside Sunday for religion, and the Jewish religion set aside Saturday. (Actually it’s more complicated than that)
Adopting the Catholic Calendar gives most places the same weeks and months, and week compatibility with the Jewish and Chinese calendars really locks in the 7-day week.
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