For much of the world, one or more religious groups with a fixed weekly holy day constitute the bulk of general society.

Because the religious make up a majority of society (and it is apparently only going to grow due to secularism failing to pass on the idea that having more than one kid matters).

Well, I suppose "How is your new datetime scheme our problem?" and "we have the numbers and we're not changing".

That's fine for the occasional festival, but for something that happens every seven days, that's a huge adjustment to make.