A common thread that I have noticed in the fans of Star Trek, Star Wars, Twin Peaks, Harry Potter and other “cultish” sorts of things is that they often attract people who enjoy messing around with codes and sets.
These are people (I’m one of them) who like arranging things and rearranging them. Who like to make categories and subcategories, and lists, and groups. That’s why it’s fun to organize star ships (what kind, how fast, how big, how old, etc), and alien races (good, bad, smart, not so smart, green, sort of like people, sort of like insects, sort of like fish), and planets, and quidditch teams.
At the same time, codes are fun. All of these cults can be seen like a puzzle, if you put the pieces together in different ways, you get different results. Some are supplied by the source material, and some by the imagination of the fans. The more you master your sets, the easier it is to compile the code (even when the creators assert that there is in fact no “answer” to the puzzle). This personality trait is also responsible for why so many fans of these cult things will agonize over apparent mistakes and contradictions in the source material, and invent ways to make the pieces fit.
Something like Forrest Gump just doesn’t have enough stuff in it to make arranging it fun.
I’m sure plenty of fans will not fit this description, however, I believe that many, if not most, fans will display this inclination to some extent. I would also speculate that the more hard core the fan group, the more they will engage in this endless codifying.
In my role of armchair philosopher, I would also assert that this personality type existed well before even the esteemed Mr. Sherlock Holmes. Back in cave days, there were probably some people on the fringe who liked to sort their rocks – by size, color, general shininess, etc. and left the rest of the cave population scratching their heads and wondering what could possibly be so interesting about putting rocks in different groupings.