I think a lot of younger people who are "interested in psychology" grow up loving the DSM because it is like a book about video game character types, like the DnD chaotic evil/lawful neutral types and a lot of confused teens love that sort of cut-and-dry sorting of people/personalities into bins that explain their behaviour. And when so many of the people who are interested in psychology have psychological problems themselves, a lot of the people most interested in the DSM are also those to whom it most applies.

Obviously for the people WRITING the DSM, it is a money-making business, and many of the people on DSM committees even admit that the process is highly flawed and unscientific, but try telling someone who has treated it like a bible since they were 13.