Because being "Attentive" is a huge part of their vocabulary. Focus is one of the necessary things you must have in marketing because if you make even a nap, All you have may you have not tomorrow.
Do not have a nap as a trader and keep working yourself too hard all in the name of a 24 hours, 7 days market and you want to make all the profit to yourself, and let's see how that is going to turn out for you.
It is a good thing though, because knowing that there is no time frame, you can always make market decisions at any point in time. However, based on what you have said, even if you take a nap, you can always have tomorrow to make a decision, so you do not have to kill yourself staying on the chart for the rest of your life.
That is precisely the good thing about having some markets open no matter where you are, that means you do not have to stay awake all the time, go and do your everyday life and trade when you are ready, trading when you are tired is a terrible idea since you depend almost entirely on your capacity to read the markets accurately and for that you need a rested mind.