It's 95% b/c ALL the schools make the kids gain an appreciation for manual labor.

If you grow up doing a job, you will respect those who do it. Same as how anyone who ever has worked as a waiter tips well and treats service staff better than someone who never has.

As a result you have decades of it being ingrained into their entire populace a personal sense of respect for cleaning and maintaining a space.

...And for the other 5%, because it is always covered in news stories every time it happens now so positively, now it's also probably a point of national pride.