1) That quote comes from his private diary. We don't know if he ever meant to share those ideas to total strangers. If you read it, you'll find that many passages are open to misinterpretation because we lack the historical context and it feels like it was written for an audience of one. He didn't choose the title "meditations", it's just what the translators and scholars used to refer to his collected works.
2) Marcus Aurelius likely didn't write that quote from the luxury of his own palace. Those writings come from his time at the frontlines of the Marcomannic Wars which lasted almost as long as his own reign. The bulk of his writing was probably written in modern Serbia.
3) Many stoic role models are anything but quiet. They die for what they believe in. They understand their own role, accept their fate (amor fati) and pursue it to the end. Cato the Younger died as a political martyr against Caesar.
4) Epictetus is another major figure in stoic philosophy. He was a disabled slave from modern Turkey. He shares many of the viewpoints expressed by the emperor, which is why stoicism is such a compelling philosophy. For something to inspire both the rich and poor, the strong and weak, there must be something to it.