Many people miss out on a lot of things by not engaging with a work and thinking through it, especially when reading. This can be said about most things in life and it can be frustrating as people tend to be biased by first impressions and don't want to analyze the totality of ideas.
Words are often just blobs, in the sense that they have meaning that is derived from context rather than their individual parts. We don't usually read each individual letter in a word, but rather the whole word, or a phrase, based on context clues. The same can be said for entire sentences or paragraphs, and so on.
Also, furthermore, psychoanalysis is based on theories of human development, unconscious drives, and the impact of early experiences on personality and behavior. And l lot of our cognitive functioning is largely based on how our brains developed.
However, if I go by that theory and apply that to this idea of skimming over text - I think it's possible people just didn't learn how to comprehend these types of things, which could be a result of any number of factors (such as teachers not caring to do so, learning styles, lack of incentive, general brain development, etc).
It can be explained by unconscious biases, defense mechanisms, and the ego-centered (narcissistic) nature of perception. People will avoid analyzing complex ideas because it requires effort and cognitive resources, which is uncomfortable or even threatening to the vehice of their very sense of self.