In the paper, The Fundamental Law of Road Congestion: Evidence from US cities, Turner and Duranton decipher this rule:

New roads will create new drivers, resulting in the intensity of traffic staying the same.

Basically adding more roads or more lanes usually does not improve the state of traffic into a city. By making it easy to reach the city, we just increase the capacity to clutter more the city.

And it's exactly what is happening with our Web pages. Browsers become more performant. So developers instead of using this extra performance to make the page extra-blazingly fast, we use it to pack more DOM nodes, CSS animations and JavaScript driven user experiences.

Why? Because we can. That's the sad part of it.

Otsukare!