As a layperson, I would have thought that not dying from electric shock must be a pretty timeless body of knowledge. So I’d expect the cost of research, writing and publishing to have been spread out over many decades, in contrast to other literature. How come the book is so relatively expensive? Does electrical code change so often?
It's something that's a) a business expense for the target group and b) something they don't really have an alternative to. It's not like you can go "nah, those local electrical standards are to expensive, I'll use the ones from Pakistan instead".
https://www.nfpa.org/codes-and-standards/all-codes-and-stand...
If you want to know the why, get the handbook too.
https://catalog.nfpa.org/NFPA-70-National-Electrical-Code-NE...
Alternatively, Epigram 48.
Good luck.