> the page is 3.1 MB in size, makes about 460 HTTP requests of which 430 are third-party requests (outside of its parent domain) and takes 20 seconds to fully load on a fast 3G connection

That's a lot of ad-tracking and ad delivery code. More than that, it's also remarkable that so much of this code is essentially duplicated. It's all user tracking and ad delivery but with each separate company loading it's own "stack" to accomplish the same thing.

It's part of a larger trend from content-centered and user-centered to advertising centered. The problem is not centralization per se but business built on advertising revenue. Facebook is an extreme example - the news feed algorithms are optimized for generating ad revenue and not necessarily favoring news reports that happen to be true.