yep, I understand your point.
I think that LD is caused by two things(except WILDS of course)
-Placebo
-Conditioning

I have nothing to say about placebo.
about conditioning, I think that the dream brain is a muscle, and it needs works, the more you excercise it(recalling dreams, improving memory, trying mild) the stronger it becomes. but yes, I know people you can LD without excercising something, and that's when this hypotesis die.
really, I don't know what causes lucidity on the dream world.
I think is the waking up of the logic part of the brain, the question is ¿Why does the logic part of the brain fall asleep and why does it wake up randomly in the middle of the dream? I think is about schemata...the brain recognices some pattern and the logic part wakes up.
I Don't know°!