Balancing a Binary Search Tree
Yes, the right subtree could be $13(10,14)$.
But notice that the article you've linked discusses the most naive version of building a Binary Search Tree, in which numbers are simply inserted into the tree one-after-another without balancing. So in your example first the $10$ was inserted, then the $14$, then $13$.
Of course there are plenty of other algorithms that balance the tree (they are also linked in the Wiki-article).