So 100% of kids reject a step-parent in all cases? You heard about it happening before, so it has to happen every time as a result?
No I never said that, in fact I even said it didn't always happen. But it is fact in recorded data that step parents and children either remain emotionally distant or take a very long time to develop a proper parent-child relationship, commonly. Rejecting blood ties as being important is wrong, they are.
The main factors that help children develop this bond is the step parents actions and the child's age. The younger they are the easier it is for them to accept their new step parent, the older they are the harder it gets.
It gets even harder with age so a girl like Minori at her age in real life would likely struggle with ever developing a paternal relationship with a step father especially as she's in early or approaching puberty when hormonal changes can effect critical or emotional thinking.
It's a cartoon so obviously it doesn't matter and again to reiterate this is the common situation but not every situation. Your personal experiences may be different but generalisation disagrees with you, just like how seeing a very tall woman doesn't disprove the fact that its common that men are taller than women.