I swear, most of the girls in this manga don't seem to have a working libido.
Adolescence is a time of bursting sexuality and raging hormones. The brains of these girls should be going overdrive with sensual urges. And yet, most of them show zero sexual reaction to physical stimuli: even when they are alone in the house with their love interest and have just shared a kiss on the mouth, they don't seem to be aware of what comes next.
Some are exceptions. There's Nao, the pervy one, and then Mio and Shizuka; they're the biggest exceptions. Kaoru, big vamp that she is, must have a sexual interest in all those girls she seduces. And Mari actually has had onscreen orgasms, helped by Yuu... who strangely never seems to be turned on by the sadistic things she does (she does enjoy herself, yes, but it appears to be purely cerebral).
And what about the others?
Everyone else's hormones seem to be out of commission. [¬_¬]