Well, it's certainly not because people actually believe capitalism is an efficient system at anything whatsoever, or whatever transparent sop Randroids sell to the plebs. What people believe has remarkably little to do with any ideology's staying power really, but more than hegemonic ideas capitalism relies on a machine which, day after day, reproduces human misery for its own sake because immiserated humans are easier to control. Thus we have some bizarre logic where the police state is sold to people as a service, and people literally pay willingly for their own poison and their own oppression (and occasionally, your choice to pay is made under extreme duress short of forcibly extracting the funds out of your account). That's the triumph of capitalism. But often critics of capitalism point to the era of robber barons when they really need to look at the consolidation of state power and the rise of these extremely massive institutions that pervade every sphere of life - for example, the state schooling system which decides what you're going to be allowed to be from about age 5 onward. There's never going to be a revolution in a society where such institutions operate smoothly, and there was a reason why when the Cultural Revolution went down in China, school was cancelled. (And no, this isn't some conservitard "public schools are bad" argument, if such a system did not exist then the state would simply write off the vast majority of the population as uneducable but compulsory schooling presents an entry point for the state into private life and access to impressionable minds, which is literally the only reason why public schooling was ever allowed to be a thing. And now that a self-perpetuating class of technicians has been built and mass armies are no longer the way wars are fought, schools have become little more than prisons for 80% of the youth in them and a moneymaking scam for colleges and the education industry.)
There are a number of other examples I can point to, but this is not some battle of ideas and framing it in such a way is counterproductive. The ideas of the ruling class are in every epoch the ruling ideas, Marx figured that shit out and there's no win through argumentation or debate on that front.