In Coelho's The Alchemist, at the very end of the journey, why did the alchemist leave Santiago alone to complete it?

At the end of the story of The
Alchemist, by Paulo Coelho, I believe that the alchemist leaves Santiago
alone to complete his journey because he has done all that he can
for the boy. Santiago has learned the Language of the World. He has already learned how
to believe in his Personal Legend. He has also learned that if he wants something bad
enough and works with the Soul of the World, he can realize his Personal Legend. The
alchemist has nothing more he can share with the boy, nothing else to teach him.
Santiago has learned, too, that he has found his true happiness and
treasure in Fatima.

The alchemist taught the boy to look
for God in all things.

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Remember what I told you: the world is only the
visible aspect of God. And that what alchemy does is to bring spiritual perfection into
contact with the material
plane.

I also believe that
the alchemist knows that to realize his Personal Legend, Santiago must take those last
steps himself: it cannot be done for him. In life, one must search for his dreams: no
one can do it for him. So the alchemist leaves, though not without providing for the
boy's well-being should he meet with trouble—which he does.
Santiago comes to understand the secret to finding his treasure, he sees the Pyramids,
and returns home to where it all began, all the "richer" for the
journey.