It wasn't super common, but it was common enough that there was a standard procedure around it (basically you'd get the classwork/homework that you'd be missing and be expected to present it upon return).

I think a bigger part now is that schools are somewhat more overloaded, so missing class puts you "out of sync" and there's nothing to help you catch back up. When I was young the parents were expected to do that: I don't know how common it is now.

Pretty much no one raised an eyebrow about this sort of thing, certainly not at the 10 day total mark.

Why do you think the rules have remained the same?

Similarly, I don't think I ever had an "excused" absence, I didn't have to provide evidence or doctor's notes to the school when I was sick. That simply wasn't a thing that was tracked at all.

1. Assimilate immigrant children into American culture so that they would think of themselves as "American" first and whatever ethnicity they came from second. (Hence, the Pledge of Allegiance, national anthem, American football games, focus on history & social studies in class, etc.)

2. Provide childcare during working hours so parents could go to work. (Hence, compulsory education, hours that aligned with a factory schedule, high student-teacher ratios, etc.)

3. Teach children the skills they would need to be successful in the factory system. (Hence, attendance, arriving punctually, moving between rooms at the bell, following orders, not complaining, etc.)

What's happened over the last 40 years is that the factory system in America fell apart, and so the skills needed for it no longer seem all that relevant compared to actually getting a good education, which school is not all that effective at. Meanwhile there are new waves of immigration with parents that were often highly educated (moreso than native-born Americans, oftentimes) abroad; they don't buy the "this is what a good education looks like" explanation, because they have had an actual good education abroad. And the Internet in general makes people much more suspicious of institutions, because you can see the ways that different power centers try to enforce control of the discourse, and there is no unified discourse to get behind anyway. The public school system in America is deeply embedded in the industrial institutions that were developed from 1900-1980, and as those institutions collapse, the public school system collapses with them.

But that's overall, in aggregate. All those drops fill up a river. But a single drop won't be missed.

And it isn't even that folks are wrong; but evidence is fairly clear that nobody has a solution for education that works. We do know of a bunch of small things that can work in some situations, but at large, we are still trying.