Because the ruling class ideas are the ruling ideas, they control education, public spaces and media (and also the repression apparatus in case the former is insufficient). We are not so different than ancient or medieval commoners who found questioning the divine rights of kings to own everything, a crazy idea.
The ideas of the ruling class are in every epoch the ruling ideas, i.e. the class which is the ruling material force of society, is at the same time its ruling intellectual force. The class which has the means of material production at its disposal, has control at the same time over the means of mental production, so that thereby, generally speaking, the ideas of those who lack the means of mental production are subject to it. The ruling ideas are nothing more than the ideal expression of the dominant material relationships, the dominant material relationships grasped as ideas.
― Karl Marx