Why don’t writers tier long sentences as Landon does beneath? His formatting is far more readable, and clarity's more important than the additional required space.
While it is a useful tool when parsing it, such a construct damages the natural flow of prose. You say it makes it more clear, but I see something that seems forced, convoluted and distracting.
He is showing how each clause has a purpose, adding description or action, improving the sense of place. I suspect he would be horrified if someone started writing a novel in such a format.
Writers seek to involve the reader, creating that sense of immersion where time stands still and you glance up to realize you missed a meal.
Lines imply a pause or breath, a change of character or action and have meaning though subtle. Choosing to have each clause and subclause have its own line would alter the rhythm of the read - potentially making the work stutter.
In poetry, word placement on a line creates emphasis and supports the meter. Such treatment of prose would emphasize everything and lose significance.
Such formatting would interfere with immersion and seem almost a parody of modern verse.
Prf. Brooks Landon does not suggest to actually write that way but uses indention to highlight different sentence structures and how they impact the flow of reading. He does not actually propose to indent in prose text but uses it as a tool to analyze the sentences. Read the first little introduction of your snippet:
We can easily see the movement of this sentence if we diagram its levels.
Put the emphasis on diagram its levels. The use of this method is in text analysis.