outsized population of kids for whom this fandom is likely one of the first things they've ever been this Big Into, so at this point in their lives the fandom/thing in question is basically their entire world and bears a similar degree of importance to them. They're young and passionate so they have a lot of time and energy to put into it, but they have no sense of proportion and are still immature enough and that time and energy are often ill-spent as a result.
They either grow out of this stage by like age 22 or blaze right through their thirties still being exactly like that.
apparently people made a big thread out of this Q while I just had it sitting in a tab to write an answer to later, oups