Why he taught in stories, in his own words.
The usual explanation is that stories are memorable, which is true and is not what he said. Asked directly why he taught this way, his answer was considerably harder.
Here are the best known of them, and his own reason, opened properly.
Therefore I speak to them in parables, because seeing they don't see, and hearing, they don't hear, neither do they understand.
The disciples had asked him why, and this is the answer. It is not the comfortable one. He is saying the stories both reveal and conceal — that a parable hands itself over to anyone willing to be inside it, and closes to anyone listening for something to agree with.
A parable does not explain. It puts you in a situation, lets you take a side, and then turns. The listener who was nodding at the older brother is the one the story was about.
That is why they survive being retold and why they resist being summarised. The moral of the good Samaritan is not the point of the good Samaritan; the question he was answering — "and who is my neighbour?" — is answered by making the hated foreigner the hero, which a summary cannot do to you.
Walking with Jesus: Devotional has a collection called The Parables of Jesus that takes them one a day, each with the question he was answering, a reflection, a prayer and one thing to carry into the day.
A one-time purchase, about five minutes a morning.