From my thinking the reason is very simple : to make people suffer from insomnia! Yes sometimes and for some persons this sentence may be rude, because they think coffee helps them to think better! But the thing that I am trying to say is that coffee destroys your power of thinking. I have never drink-ed a one single glass of coffee. It might seem to you now that I am too young that I am not drinking. Yes I am too young but people younger than me have used coffee to enable insomnia for themselves. Like this :
Sometimes coffee seems very good and very helpful, and sometimes and somethings have their side-effects with their benefits. I have experienced and others have experienced things like coffee. The best example would be : Using medications. Drugs or medicans can give you a moment of relaxing. But they also have their side-effects and sometimes they are very dangerous. In Afghanistan drinking coffee and other high caffeine drinks are very usual and it is not important that how much old you are? And they drink it. I am saying that even when you are in very need of it, don’t drink it. And I am not insulting those people which drink coffee or energy drinks. It is just a friendly suggestion or you may say advice. Same as harmful drugs that people get addicted you will get addicted to coffee and energy drinks.
I would like to give you a great example of coffee and medicines : When you have a headache you use a painkiller drug or any other kind of drug that calms you down, see it calms you but the pain is still in the position , you just don’t feel the pain (ache) that’s all.
Same is with case of coffee and let me give you a example of that : When you have an important assignment for you class tomorrow and you haven’t done that by 9 o’clock (PM) you immediately think of being wake till midnight to complete your assignment. And the only way for you is that to drink coffee or any other energy drink. So you drink a good cup of coffee and you don’t fall as sleep because it contains very high caffeine. But still you have that feel of tiredness. It works that same way as painkillers. You have the sleep need, but you just don’t fell as sleep. Because you drink-ed something with very high caffeine.