Perhaps a country with a higher proportion of regular church attenders (past as well as present) will have a higher proportion of people who "spent their formative years singing from hymn books", and consequently a higher proportion of people who find it natural to sing from a book.

And such people may often have learned how to sing with meaning and expression from the book, and will be equally baffled by people who haven't learned to do it effectively and by people who refuse to believe it can be done effectively. A background in church attendance is not necessarily bad for musicianship.