It is best to start this answer with a brief introduction of Gordon Allport. He was born in 1897 and he died in 1967 and he is seen as a pioneer in the area of personality psychology. Some see him as creating this area of study. He also published widely both books and journal articles, and he taught at Harvard for the bulk of his life.
While his name is not as famous as Sigmund Freud, Allport's influence is every bit as important. It is not an exaggeration to say that his theories are deeply ingrained in all of us. For example, he is the one who emphasized the importance of the concept of "self esteem" and the notion that all people have different dispositions. He also emphasized the important truth that all people are unique in the world of psychology. In addition to all of these points, he also taught a generation of prominent younger scholars.
In view of all these points, people study Allport for several reasons. First, he was an original thinker, whose writings are important to study to understand people. In a word, there is intrinsic scholarly value in his work. Second, as a foundational figure, if anyone wants to understand the history of psychology, Allport is a must read.