First, the author is clever. Many people's portraits have the same characteristics. Some ancient officials wrote about beards in some books, but they didn't generalize about other faces, so they just wanted to describe other similar characters through a decent template. Then describe some small details of each person, so that we can distinguish their specific dynasty from their personal character. For example, we can describe a person's personality from the eyebrows, and we can distinguish the dynasty in which this person lived from the aspects of clothing and hats.
Second, it is convenient to resemble people. Because there are so many characters in the book that they need to portray, if everyone wants to deepen the details, it will be very troublesome, so they simply unify their expressions and expressions. Such unification will make people feel that the people in our history textbooks are exactly the same, and we can judge that they are not the same person only with some obvious clothes and headdresses. Coupled with ancient portraits, it will do great harm to our eyes now. When restoring portraits, people may not pay much attention to the preservation of portraits, so it is easy to restore people in portraits into public faces.
However, if you carefully identify this person, you can still determine which ancient person he is. So it's not that they are exactly the same, but on the whole, they have many similarities.