Yes, you are right that the shift was at least in part triggered by the disrepute into which some of Plato’s ideas (e.g., the Forms) had fallen. It was an attempt to get back to the “skeptical” Socrates, the one who knew that he knew nothing…

As for it being the result of the actions of a single person. Well, so was the finding of Pyrrhonism, or of Stoicism.