Frank

Six day week is superior to seven because a prime number week is stupid. There's a lot of things that people like to do every second or third day; in a six day week, this is always the same days each week.

All months are the same length. Advantages obvious.

Thirty days is a good round number for a month; it can be divided into so many smaller numbers. Convenient for things that need to be done regularly; you can do them on the same days each month and have the gaps between them all exactly the same.

Every month in a given year starts with the same day. If the 3rd is a Wednesday, every 3rd will be a Wednesday. This is a massive help in scheduling bullshit that ends up happening "second Tuesday of every month" or whatever, and also helps people track regular monthly things (if you have a monthly meeting on the 15th, it's going to be the same day of the week every time). Fitting weeks perfectly into months just offer so many improvements for scheduling and remembering stuff.

The days move back with each non-leap year -- if the 1st of every month in 2025 is a Tuesday, the 1st in every month in 2026 will be a Monday. (This also happens with out current calendar as neither 6 nor 7 fit into 365). This means that if your birthday is on a Monday or whatever, it won't be that way every year -- only the same day of the month WITHIN THE YEAR (2 years in a row for leap years) is the same. (I bring this up because last time I mentioned this people didn't do the math and thought that the days of the week would be consistent across years, somehow, mysteriously).