@Makenai
Because the shitty author developed all the losing heroines up so much that tossing them away in a shitty ending (especially after the future dreams) like this would piss people off? (Chisaki lost Kogarashi THREE TIMES now in the course of this manga thanks to those future dreams)
Because it was ONLY thanks to the other girls and their love for Kogarashi that the day was saved?
Because having the future dreams arc and having Kogarashi remember each and every future where he fell in love with the girls only to say "I only really cared about saving Yuuna tough shit" is shitty?
People didn't want an "open" harem ending, they wanted a "conclusive" harem ending where all the work and sacrifices the other girls made for things to turn out better than the alternate futures would actually be rewarded and mean something instead of the hack author tossing them to the side once they served their purpose in making it possible for the two leads to get together.
Plus this stupid ending had Oboro do a total 180 from her regular personality to "harems bad" as one last fuck you to the readers and the fans of the other girls to make it absolutely clear that there is zero chance the loser protagonist (who never had any internal monologues or visible character development to show his feelings towards the other girls and how/if they ever changed) would actually change his mind.