If you suffer from thought overload when you're trying to go to sleep, or if you wake up in the middle of the night with the urge to put your thoughts down on paper (like I do at least a couple times a week) I think I have the answer to why. My answer comes in the form of a question or three. How much time do you spend with your thoughts during the day? Do you have regular time set aside each day or week to decompress and journal your thoughts? Do you take regular time to sit before God and examine your life? Maybe we lose sleep because bedtime is the only time we have to decompress. I really believe that every person should examine their lives and be alone with their thoughts on a regular basis. I find that when I have this regular time I actually sleep better. I'm able to go to bed without stressing over what's going to happen when I wake up. Give yourself time to fully express yourself while you're scheduled to be awake.
I'm sure I could do a much better job explaining this, but I've been up since 4 am.