Probably a selection bias, most (all?) ancient works we have were copied by hand (expensive!) and widely circulated enough for us to still have them. So we still have Marcus Aurelius but not Caesars poetry.
This is definitely the case. Most ancient texts were not lost in the burning of Alexandria or whatever, but simply decayed. The texts have to be actively copied to be preserved, and there was not the money to do this continuously over 2000 years. So only documents that the rich of times considered most important to be preserved were copied.
On the other hand, we still only have four out of the eight books of Epictetus’ discourses. (He’s another stoic philosopher and his discourses had a similar impact on me as meditations had on you.) This seems to refute the strong version of your argument.