Iiwake Maybe because;
1) it gave me a catchphrase I can actually use in real life (maybe, maybeeeee)
2) no other single will ever come close to the utter spectacle that was the election proses and the reactions to it. idol songs for me are just a means to see the girls do their stuff.
p.s. i forgot, it was also the first to recognize that the non-senbatsu girls had fans (undergirls)