[yadingus]

From direct observation, people who are persuaded astrology tend to know a lot of people. You could say a sort of map to observe and predict relationships across all the people you already know and all the people you will meet is useful.

Conversely, people who are very outspoken against astrology don't have as varied, dynamic and big social circles. Hence they'd not need a "social map", and they might even lack the social intelligence to realize that other people do.