Why were we teasing a genuine romance with Nakano if we are just going to do a harem ending?

I'm pretty dissapointed honestly

I think the author wanted/had to end it quickly, thought the romance wasn't developed enough and that there wasn't enough chapters left to do something conclusive.

So they went for a quick harem end. The ending arc dilemma was only 3 chapters it might have been something else if there was more.

I've got the Avatar The Last Airbender "That can't be it, where's the rest of it" meme playing in my head right now.

This series is character of the week with a loosely connected plot and minor Nanako subplot so harem ending was the best way for it to end. It could have been better with interactions between other girls in the club but it was never structured that way.