Officials are usually elected because the people trust them (yes von der Leyen indirectly elected, but that's besides the point here). In geopolitical decisions for example, the people can't and shouldn't be able to know everything.
Trust is a process, not a static state. In order to trust someone you don't personally know, you usually need some level of transparency. Perhaps not total (as you mention, there is genuine need for some secrecy in politics), but surely much higher than the required level of transparency of random citizens.
