So this is where the ship's popularity all started from, huh? Or this doujin, being one of the first NicoMaki works, helped with the ship anyways. I can see why, this really was good.
It was the most popular ship from the get-go (especially in Japan). One reason is probably that, while they like Maki about as much as people in the West do (a lot!), in Japan they're very fond of Nico as well, she's usually just down a notch from Maki in popularity.
Not only the manga, but some of the diary and drama CDs, are by the creator of the yuri series Strawberry Panic, and she's always shipped NicoMaki pretty hard.