It is not so much that religion, as expressed in these texts, has so much power, it is that "the masses" have so little power. The more people are oppressed and rendered powerless, the more they turn to something, anything which gives them "power," no matter how illusory may be that power. For some it is religion, some it is science, some it is "opium" (or a modern day derivative of), or politics, or, ... or ...
See Marx's quote below - part of which, is familiar to us, and always taken out of context.
"Religious suffering is, at one and the same time, the expression of real suffering and a protest against real suffering. Religion is the sigh of the oppressed creature, the heart of a heartless world, and the soul of soulless conditions. It is the opium of the people."
http://www3.baylor.edu/~Scott_Moore/texts/Marx_Opium.html