It is known as de-sensitivation of a national identity and should be reserved for very few occasions.
It has become so common that nobody even notices or cares anymore.
I'm wondering why the flag is raised at all anymore. Nobody notices but me and a few military veterans.
We moved to a small town in Ohio 6 yrs ago. The flag in our local cemetary has been at half staff for all those years. Like you, I’ve asked and no one seems to have an answer.
When we grew up half staff actually MEANT something.