Technocracy always struck me as weirdly incoherent? If you take the economy, probably the most studied of government policies, it is not 1 number. There are many questions about what priorities ought to be. There is no 'expert' answer for how many starving poor people are a worthy trade off for a GDP point. Even if there was, there is an economist branch that disagrees with any possible position you might take. The question of which experts to listen to almost entirely subsumes the question of what experts say. More than anything it's a branding strategy. "Putting me, a surveillance investor, in charge of international relations is clearly more rational and scientific than putting the other guy in charge."
My theory
It coalesced at a time when science was becoming more accessible to the masses, more educated technicians running around engaging in work and trade.
And these technicians were frustrated by bosses who didn't understand the science and technique behind things.
So there was great inefficiency because the bosses hadn't caught up to the technicians in their understanding of the world.
And so the political idea of "put in charge the people who actually understand the problem" caught hold of the technicians, and they were fired up for a period of time and they called it technocracy.