A summary of sociologist Robert Bellah’s life in the New York Times includes this observation about studying religion in sociology:

He was widely credited with helping usher the study of religion — a historically marginalized subject in the social sciences — into the sociological fold.

This begs the question of why the study of religion within sociology was marginalized in the first place (and also perhaps whether it still is today). It is hard to escape the topic from reading the classical theorists, like Durkheim, Weber, and Marx. Perhaps this is a self-fulfilling prophecy of secularization within sociology?