为何外国人喜欢早上洗澡？

Why do most Americans take a shower after they wake up in the morning?
为什么大多数美国人早上醒来之后要去洗个澡？

I'm Chinese. What I know is that nearly all Chinese people take showers at night. Why do Americans take a shower in the morning which drives them to wake up earlier? And I also want to know which countries take a shower in the morning like America, and which countries take a shower at night like China.
我是个中国人。据我所知，几乎所有的中国人都是晚上的时候洗澡。为什么美国人大早上地洗澡呢？这能让他们醒得早一点吗？还有，我想知道哪个国家的人像美国人那样早上洗澡，哪个国家又像中国人那样在晚上洗澡。
 
获得1.3K好评的回答@Kaiser Kuo

I'm an American-born Chinese who has lived in China for a total of over 20 years, so this is a question that I get all the time. Among everyday habits and, the shower-in-the-morning vs. shower-in-the-evening is one of the real lines of demarcation between Chinese and westerners, and neither my Chinese-born parents (who never lost the evening shower habit even after 40 years in the US) nor my wife, who's from Beijing, ever get tired of asserting the supremacy of the PM shower. And I've never kicked the AM ablutions habit.
我是个在美国出生的中国人，我住在中国已经20年了，所以这是我一直以来都有的问题。在所有的生活习惯中，早上洗澡跟晚上洗澡成了中西方人的一个真正的分界线。还有我中国出生的父母（虽然呆在美国40多年了，但他们还是一直在晚上洗澡。）跟我来自北京的妻子，都从未改变晚上洗澡的习惯。而我从没改掉在早上洗澡的习惯。

I shower in the morning because it really wakes me up, and provides me with this nice mindless routine during which I can think about my day. It also keeps my hair from looking strange. On warmer days where I've conspicuously sweated during the day I'll take a quick shower and not wash my hair in the evening, but I find that taking a shower right before bed makes it more difficult for me to fall asleep, possibly because I associate showering with wakefulness.
我早上洗澡是因为真的能让我清醒，可以让我认真想想这一天当中毫无头绪的日程。这也能让我的头发看起来不一样一点。天气暖和一点的时候，白天显然出汗多，晚上我就快速地冲个澡然后不洗头，但是我发现睡前洗澡让我更难入睡，可能是因为我已经将“洗澡”和“清醒”联系到一块去了。

I fully understand the Chinese preference for the evening shower. You're clean and comfy, bedding probably doesn't need to be washed as frequently and so forth. But I just need that morning shower to feel fully awake—kind of like that morning coffee!
我完全理解中国人晚上洗澡的喜好。你身上会很干净还很舒服，那样你可能就不用频繁地洗那些床上用品等等。但是我需要早上的沐浴来让我完全清醒——就像早上来杯咖啡一样。