-Chocolate Box's higher signup count means there's proportionally more casual participants compared to hardcore treaters
I think this might be the main reason. The first year there were more than twice the number of fics than the number of participants (292 sign-ups, 617 stories), then the number of participants increased and it was a worse ratio (404 vs 775). This year we'll see if there's a correllation, but we'd still need another 80 fics to get twice the number than sign-ups.
Re: Almost Chocolate Box Time
I think this might be the main reason. The first year there were more than twice the number of fics than the number of participants (292 sign-ups, 617 stories), then the number of participants increased and it was a worse ratio (404 vs 775). This year we'll see if there's a correllation, but we'd still need another 80 fics to get twice the number than sign-ups.