Because unless you start fining or imprisoning people for using the wrong date format, people don't care what you write in a law book and will continue to use w

Because unless you start fining or imprisoning people for using the wrong date format, people don't care what you write in a law book and will continue to use what they're used to if it works well enough. Allowing DIN 5008 simply acknowledges reality. Not acknowledging reality is a good way to make people decide that whatever is telling them they're doing it wrong is just "ivory tower" nonsense and should all be ignored at best, possibly actively opposed.