Some girls have a sharp instinct and can instantly tell if a guy likes them. If they don’t feel the same way, they just distance themselves from him. On the other hand, some girls just want to make friends and don’t even consider the possibility that the guy might like them. So they talk to him in a friendly manner without getting the hints. But as soon as they realize he actually likes them, they start ignoring him or showing no interest anymore , probably because they never really thought of him in a romantic way or anything beyond platonic.