Nobody Knows might not be a plot driven film, but it had a classic narrative struture w/ character arcs and a strong dramatic premise. I don't agree that Nobody Knows is about "the happening of daily things" since mother's don't usually abandon their children for six months, but even if it were about everyday life, Japanese directors like Ozu and Naruse were masters at showing the repetitions of everyday life while maintaining narrative economy. 

In the end, we all have our own sense of filmic rhythms and if it worked for you and the audience you were in, I'm happy to hear it. Personally I think Kore-eda was caught up in his themes; themes which are often more resonant if you cut to the heart of what your film is about. 

It was a wonderful film, though, even if I think he softened the tragedy.