People looking too deep in number of chapters... you know, maybe, just maybe, it's because the plot of her arc is bigger? Ichika's, Miku's and Yotsuba's arcs were just conclusions to their respective character arcs, Nino's was a conclusion to her arc as well as conclusion to Maruo's arc (later has been built up for a long while so it did not need extra content and could seamlessly be merged with Nino's arc), whereas Itsuki's is conclusion to her character arc as well as both start and end of the arc about their biological father who BTW is a brand new character (and in extension is also resolution to their mother's arc). Unless you want to turn the story into rushed crap just to stay consistent to chapter numbers, you need to spend more pages on this arc.