Well, yes, he's turning the things he got from his teachers into aphorisms and rephrasing them to keep them fresh in his head without turning them into words to be repeated out of habit. It was his journal and not meant to be read by other people; he didn't need to explain things to himself at length, just to remind himself. If you want a lengthier explanation, Epictetus is one of his student's notes from his lectures, and is meant to be instructive, and Seneca is as verbose as anyone could ask for. None of them are up to modern standards, because even philosophy has made some progress over the past 2000 years, but there are books that are meant to do what you wanted Meditations to do. Meditations just one of them.
But do read Pierre Hadot's The Inner Citadel for why Meditations isn't as shallow as it looks.