There are two major categories of people who typically buy college gear.
The first category of people who typically buy college gear is that of (current) college students. These tend to buy college gear bearing the names of the colleges they attend. Others buy college gear bearing logo graphics associated with the colleges they attend. From those things (the college names and logos in the college gear) the students are able to gain a sense of identity.
The second category of people who typically buy college gear is that of people who are not college students, but who nonetheless find college gear trendy. Some of them turn out to be previous students (alumni) of various colleges, who buy college gear associated with their alma maters for, among other things, identification purposes. You come to realize that many people have some very deep attachments to the colleges they attended. One way in which they are able to keep the connections alive is by buying college gear associated with their respective alma maters. But we also have some folks who did not attend any prominent colleges, who nonetheless feel inclined to buy the trendy-looking college gear. This is because college gear is considered fashionable in certain social circles.