Indeed, why does a painting or sketch of something often look better than the thing itself?
I don't know the precise answer. But I am reminded of an anecdote an old friend of mine had once shared with me.
In one of those North European countries (I don't remember which), there happens to be a community of artisans specialised in making wooden toys. My friend, one day during one of his trips to the place, stood watching a person making a wooden horse with fascinating precision and speed, almost hard to believe. After a while, my friend couldn't contain himself and asked the craftsman how he managed to do such a hard thing (building toy horses) with such ease. The good natured man smiled and said in his accented and broken English: "Not hard at all. Not hard at all." Then picking up a block of wood, he said: "Here's wood. You just have to remove what is not horse. And there! You have your horse!"
...and this story seems to be a block of wood hidden in which seems to lie the horse -- the answer to the big question: 'Why does a painting look better than a scenery?'
In every block of wood that passes before our eyes, there's hidden a horse. An artist, in some way or another, just takes that horse out and presents it to you. In every scene that passes before us, there's a painting hidden. An artist just takes that painting out for us. By highlighting what's interesting. Abstracting away the rest. Often, he highlights what could be interesting.