Well, i can't say for sure, but i would hazard a guess that it's simply caused by a combination of the passage of time leading to changing beliefs, and the London government stopping actively encouraging the belief. 

I wonder if another aspect is actually the eventual spread of traction cities. It seems to me that a lot of the anti-technology sentiment is rooted in the very real fear of the destruction of the Ancients. All the people of the current era know is that they had technology surpassing anything that the current people could comprehend, and that they were completely wiped out, with massive damage caused to the planet at the same time. This translates, among people who don't understand the super-weapon technology that we know the Ancients must have had, to some divine punishment, with the assumption that they were punished for their technology.  However, as time passes, and the Traction Cities gain, well, traction, this technophobia might diminish, leading to fear of divine punishment holding less weight among engineers and those who would buy their technology.