You make it sound as if the natural growth in technology is what makes these websites huge. I run a web app, which is uptodate technology-wise. It has a responsive design with @2x images and @3x. It uses JS in a sensible manner. It's fast and easy to use. Top notch technology. Yet, the average request sums up to 200KB. And 60KB of that is a custom font.
This is not about the natural growth in technology, it is about 50-70% of the 2MB are entirely worthless to the user, because they are usually Ads, trackers, wrongly compressed images (ImageOptim does wonders here) and using 10 JS frameworks in parallel.
It's almost as if you're saying: See, img tags now support the width attribute, so let's upload a 10MB photo and just tell the browser to resize it to 100px, because technology.