National Public Radio asked exactly this question in a survey a year or so ago and they got the following principal responses back.

国家公共广播电台问过,完全相同的问题,在一次一年前的民意调查中,他们得到了如下的回复

耶鲁公开课 - 聆听音乐课程节选

A seed,a strength,a virtue,a competence that other teachers did not see, because they did not ask this question; because they asked,metaphorically speaking, ?" "how many geometric shapes do you see on the screen?"

潜能，优点，品德，能力,这些是其他老师没看到的，因为他们没提出这个问题;,打个比方，他们只会问，“你在屏幕上看到多少个几何图案“

哈佛公开课 - 幸福课课程节选

Now the people in this poll were asked the same question and here's what they said, so 75% said that one reason is that it's more convenient, it's what people like to eat, it's heavily advertised, it's more affordable, people may not know which foods are healthy.

在这个调查中人们也被问到了这个问题,我们来看看他们的答案,75%的人说选择垃圾食品是因为更方便,合乎口味,广告的大力宣传,更便宜,人们可能并不知道哪些食物才是健康的

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选