Fallacious syllogism. The Egyptians were polytheists with equally fragile deities, yet their priesthoods were tightly aligned with their ruling class and most certainly controlled the populace. Likewise, Native American religions were certainly polytheistic, still carved in stone in Central and South America, yet their priests were similarly aligned with the ruling elite. What a shock that power aggregates in the institutions of a social order -- duh.
It is some sort of wishful thinking that casts about and tries to find the bogeyman in modern religion. Methinks it is the sour grapes of aftermath following the delusional euphoria of the 60's that religion was dead and dying. It was too easy to dismiss the importance and sway of religion by opining about it as if it were elderly and toppling. It was a progressive and Eurocentric view that was also adopted by much of the coastal US intelligentsia. Nothing could be further from the truth.
And to this thread's stated topic, it was in part due to the fracturing of American religion, moving it away from the mainstream monolithic image and into the reality of many sects and their diverse manifestations. Protestantism evolved away from the bourgeois mainline denominations that had co-opted the vitality of religion with mere social convention, and it moved off to the burgeoning Pentecostalist and Fundamentalist sects that reshaped the face of religion in America.
Likewise, American Catholics were the driving force in the changes that culminated in Vatican II which closed in 1965. To the credit of the Papal See, the ancient church lurched forward in a hotly controversial move that is still seeing aftershocks of adjustment and rebuttal within the largest religion on the planet. The change made the institution once again adaptable to the local populations the world over, one of the traits that has in fact continued to propagate the Roman Church.
Elsewhere in the world, Islam continued to widen the divide between Sunni and Shia, an internal struggle, but important, for it reveals that Islam is not monolithic either, and mutates as it spreads, a reaction to biases on the part of cultures that adopt it. This is even more evident as one looks to Indonesia and Sufism.
Strong cultures, including religions, survive because they adapt as well as provide to their populations what their cultures demand or want. They don't stand empty in the 21st century with empty pews and coffers because no one attends. Railing against Islam or Catholicism as some sort of unique or singular actors is a bit naive. The force of dominant social institutions has always been mirrored in their religions.