I'll be honest, schools are underfunded in Japan too. Too many pensioners eating up the national budgets
https://www.weforum.org/agenda/2019/10/education-spending-highest-school-brazil-chile-italy-mexico/
Very similar levels of spending for primary kids; Japan's looks a bit lower.
It's partly about prioritization. School systems that think of textbooks as an unthinkable part of education that can't simply be opted out of, spend on them and not on other things; Japanese public schools are really dingy looking, so much grubbier looking than UK ones, have bigger classes (35-40 is usual) and have less tech - actually, close to no tech at all, frankly. They do have textbooks and it's just seen as something which you can't "do" education without; a school with no textbooks would be the next thing to "a school with no teachers."
UK schools, which I've also spent a fair bit of time in, do not have textbooks much in evidence; they are smarter looking (at any rate, a lot less dingy and run down looking than Japanese public schools), have nicer playgrounds and a lot more technology, and the classes are quite a bit smaller.
Personally, I think the textbooks are a better use of money, but I guess different cultures prioritize different things.
When a country has a curriculum set in stone, setting out in concrete detail the actual content to be covered at each level (not just aims/skills), this means private industry is able to produce things like workbook that align 100% with the curriculum. I can go to a bookstore here, grab a 5th grade science workbook, maths workbook and literacy ("kokugo") workbook off the shelf, and know that everything's aligned with what they are doing at school. I've never actually taken my child out for a long break, but do know parents who did do this, and there were no issues, and the teachers did not need to do anything in particular. I've always used the shop-bought curriculum-aligned workbooks to support my child's learning anyway, so they usually know stuff before it's covered at school, as do most remotely competent parents in Japan, including foreigners. So if I suddenly did take my did out for a bit, no big deal.
FWIW, I think English schools are mostly really good and the teachers do a sterling job in pretty hard circumstances, but if I had to make one criticism, I do think the lack of textbooks, lack of books coming home daily for parents to see, and lack of a really content-specific curriculum is one weak point. It encourages a very infantilized attitude among parents, where they don't really know what's going on in their child's curriculum, don't take charge of their kids' education, and just sort of expect the teachers to do everything for them.