Diplomatic actions (raising/lowering loyalty/sympathy) are more effective if you are an Ambassador. Though why being an Ambassador helps more than being King does I don't know (well, I do, because no one wanted to code for that case, but IC I don't know).
Not so much "didn't want to" as "didn't think of."
Being Ruler should, indeed, lend at least as much weight to your diplomatic actions as being Ambassador.
