You might as well ask why the birds all sing different songs. I don’t think anyone chooses to be a mystic, it’s a type of spiritual talent I think, in the same way that some people are just incredibly gifted singers or musicians seemingly from birth.
I’m not making the claim that mystics are in any way better or more spiritual than anyone else, spirituality comes in many forms. Talented musicians, painters, writers and artists of all types are equally spiritual. Good art is always a from of mysticism.
A mystic never discovers anything new, all that he or she can do is uncover what is already known by the soul. It’s not that God reveals himself in little steps, or one shade at a time, but rather God leads you on a journey of comprehension one small step at a time.
Like Moses in the book of Exodus, who asked to see all of God’s glory and was placed in the cleft of a rock and covered by the hand of God so that only a tiny fraction of his luminance and goodness passed through. Anything more would have destroyed him, God gave Moses as much as he could handle, but not a fraction more because it would have put an end to Moses, not through vengenace but through love.
Everyone’s journey differs from each other but the end result is the same. No man alive can possibly hope to understand all of God. To see more than you are capable of seeing would be the equivalent of gaining unearned wisdom which is a terrible thing. The mystic walks the thin line between sanity and madness, law and chaos, love and destruction, but it’s a line worth walking.
Mystics mine spiritual diamonds and lovingly and reverently share them with the rest of humanity.