On the sleep deprivation topic, adenosine buildup in the brain is, along with melatonin, one of the brain's core sleep mechanisms. As you expend energy during the day, adenosine builds up, so your brain has an idea of how long you've been awake.
Creatine recycles adenosine back into ATP, so less adenosine builds up. The amount of creatine you find in foods naturally is way less than the amount people are supplementing with.
So it makes sense physiologically why mega doses of creatine might negatively affect sleep.
So creatine adds the phosphates back to the adenosine? However, it's a good reason to exercise. Burn the phosphates from ATP and be left with adenosine, which as you say promotes sleep.
However, I don't think it is so much of a signal of your brain having an idea of how long you've been awake, that's the circadian cycle. I always looked at adenosine as a driver of sleep need. If you burned this much ATP, we're going to need to recover. Seems like an elegant process.
As with anything in medicine, if it was that straightforward, someone would've already discovered that right now. Human physiology (and biology in general) is such a messy field that the simple act of using isolated facts very rarely gives useful insights.