"Because I said so," ends our inquiry, shuts the door and disrespects the questioner, all at the same time.
Explaining what we need and why allows us to engage. It creates a connection of mutual respect.
When a bureaucrat or authority figure refuses to explain 'why', he is showing fear (because he's not sure why) and contempt (because he doesn't have to care).
We'd prefer to engage with a human, every time.