This forum is small community of various individuals that share at least one bit of commonality, an appreciation for Jim Butcher's work. Though, we do so in different ways. I, myself, fixate on the unsolved mysteries of the series; others have their own interests. We share what we think and what we like while being receptive to what others think and like about the works.
I cannot speak for others; but, I often develop strong attachments to other fictional works. I love early Stephen King, I have read a large number of Dragonlance books, and I have been a comic book fan for over 30 years. Do I visit forums related to these works? Nope. Why? Because I do not get the same communal feeling that I get here. In the series, the first time that Harry walked into Mac's bar, he felt as if he had rediscovered an old home. My feelings are similar to that feeling.
If you don't get "the appeal of this series that induces the great interest;" then why visit the forums? I am here because I get the appeal. I think that many other members do as well. But, hey, the ratio of male members to female members is 29 to 1 or so the statistic center states. So, "maybe it is a guy thing?" Though, the person with the most posts here is female. So, I could be mistaken. I often am mistaken; but, I still keep trying to make sense of things. Did this help?