Exactly, if you want to create a website for your high school chess club there is a ready made solution that while not perfect is fairly difficult to beat by hand. So the average became more complex because the simple problems had already been solved AND you are building generic solutions to cover more areas. In other words Facebook solved a lot of the problems people used to learn HTML to solve and now Facebook needs a few high quality designers not just a HS student with some time on their hands.

Net result fewer people learned HTML because it was not needed.