I simply think that the word reason is a poor choice of words.
I don't see why it is open to interpretation. Things don't have to have a reason. Besides, we know why evolution happens. Those "mechanical and chemical aspects that shape the process we call evolution" are the reasons for evolution occuring (if I remeber the post that you were replying to correctly).
A much better choice of words is perhaps not "the reason or reasons why"
but HOW evolution happens as we understand it.