In the not serialized chapters only one member was necessary, right? Some space for a new character to come in, which is probably a good move to keep the series going.
@Takkero This author is doing the same with Takagi-san, and not only has the manga surpassed the 100 chapters, it also got an anime adaptation and two fan-made spin-offs.
When you only have slight to no interest in x person, but he/she is interest in you. You will also show interest to the x person too sooner or later. Well, if the appearance and personality somewhat fit the condition.