Just because one is an emperor does not mean they can suddenly solve any problem. This is precisely what Aurelius' writings [1] focus almost exclusively on. In spite of being the most powerful man in the world he found himself to be quite helpless in terms of actually improving the state of mankind which was his genuine motivation. As a peer comment mentioned, these writings were never meant to even be seen by anybody other than himself. They're effectively his diary.
He found himself not only largely unable to help better mankind, but could not even better his own son. Aurelius is generally regarded as one of the greatest leaders of humanity to have lived; his son (Commodus) - one of the worst. Father deified, son assassinated (to great celebration) and struck from all official record.
And it wasn't simply failure to achieve, but also failure of circumstance. He was surrounded by death which climaxed with a many years long plague that by some estimates killed more than 30% of the entire empire's population, including some of Aurelius' own immediate family.
[1] - http://files.libertyfund.org/files/2133/Aurelius_1464_LFeBk.... # That book has a lengthy, and necessary, intro (well multiple actually) explaining stoicism and providing various historical context. Aurelius' writings themselves only begin on page 25 of the book, 59 of the PDF.