I think the prior comment is pretty spot on. It's hard for me to think of anyone I might ask for something and not feel annoyed or even disrespected if I was given absolutely no explanation. Even if I had reached out to someone I don't know, basic politeness would dictate some sort of reason even if it's a "sorry I don't have time for that right now" or even "I'm just not interested in participating".

If I actually knew the person, a "no" with no explanation would virtually always have negative consequences. To a boss, it would likely be insubordinate. From an in subordinate, the same and would likely elicit a "I beg your pardon?" From a friend or colleague, it would cause me to question our friendship.

In the modern world, politeness is largely built on a willingness to explain and give verbal consideration. Not doing so will often (if not usually) feel disrespectful or like some sort of power-play.