> When did the industry put the onus on the user to understand how the computer works?

Just after the turn of the century, that was when there was a big shift in the industry to move all user interface design work to artists, and away from original user interface specialists. The whole profession of user interface designer (one who understood "form follows function") ceased to exist in the early 2000s, as all work was assigned to graphic designers (who only understand aesthetics).

This movement can be seen clearly in the evolution of widget toolkits for desktop applications, which peaked in usability in the late-90s/early-2000s, and have been losing usability while getting prettier with every iteration since.