There was nothing, technologically or organizationally, preventing web development from becoming so complicated, such that websites whose desired functionality would be satisfied by static html are now several meg of thousands of lines of javascript on top of a few dozen included libraries. There was nothing preventing that. Therefore, it happened.
Developers don't really feel like pointing out, "you should get rid of me and just pay for someone to do html". Managers don't really feel like pointing out "the project I'm managing doesn't really deserve a team of developers, you should take them away from me." The designers don't feel like pointing out "all we really need is to put this well-formatted text on a page with the company logo on the top and one or two image files, and that will communicate the information just fine, you can get rid of me." The even-higher-ups don't really feel like pointing out "I don't need to hire all these people, you can take this VC money and return it to the original investors". The VC's don't feel like pointing out, "there's not really a use for this much money in the tech world right now, so you can just stick it in a bank account and wait for a real need."
So, it doesn't happen, because there was nothing to prevent it.