The reason is simple but to answer your question wouldn't be as simple. Also, I can only try to explain it to you in simple terms, so please bear with me.
It's because of how my dreams functioned for me personally.
Years of having (almost) countless supernatural attacks led me to my current spiritual master in 2007, who taught me ways to protect myself against such attacks.
I didn't get to chose it for myself, the same went for my master as he just let things flowed naturally for me, but I then seemed to have developed a way to fight off supernatural attacks in my dreams.
I'm but a normal person with no gifts of seeing or hearing 'them' with my waking time consciousness. Thus for this way to work to the most of it's effectiveness, I guess it has to be my sub-consciousness that is instead taking control over my dreams, which makes sense to me.
If my waking time consciousness taking control over my dreams, I'm afraid there's always a chance I'd make mistakes when I had to fight off negative entities in my dream; the same with the mistakes I'd tend to make during my waking time (you know, like, mistaken a foe for a friend thing).
Not to mention by considering the fact that I've developed a way to fight off negative entities (or person(s)) in my dreams, you can say my protection in this matter would also rather thick that it wouldn't be just your 'normal average people' that can leisurely walking in through my dreams.
And to tell the truth, ever since I developed this way of fighting off negative energies in my dreams, I've crossed path with quite a number of unknown persons in my dreams. Some turned out to be the enemies, and some others turned out to be my spirit guardians sought only to speak with me in those dreams. You can imagine it could be a nightmare should I mistaken a foe for a friend here; I might have tried to take on my own spirit guardians or caught off guard by the enemies, I don't know which one is going to be worse. But I'm sure you can imagine that a slight mistake you made in this department can be fatal for yourself.
My sub-consciousness on the other hand, wouldn't make as much the same mistakes in this matter; it seems to know how to detect negative entities or ill-intentioned person(s) in my dreams early on and told me how to address the matter accordingly as quick as possible before it escalates, somehow. And it just happened automatically as in I don't have control over it consciously.
And that's why, for myself personally, I'd be glad to just leave matters in my dreams under the control of my sub-consciousness instead, since I have to always be extra careful with and in my own dreams so to say
Thank you for reading
Salam,
Astra